Vulcanized Conveyor Belt Splices

kennygu · 发表于 2010-2-2 22:33:13

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Vulcanized Conveyor Belt Splices

Vulcanized splices provide a method of joining the ends of conveyor belts without interrupting the continuity of the belts, and usually without altering the geometry or dimensions of the belts. Modern conveyor belts, made with synthetic fabrics and normally having high adhesion between components, lend themselves to effective and long lasting vulcanized splices. There are some types of conveyor belts that can only be spliced by vulcanizing. This section of the Conveyor Belting Engineering Handbook is provided to give an overview of vulcanizing. Details are available from belt manufacturers, their authorized agents, and splicing contractors.

The underlying principle in vulcanized splicing is the establishment of adhesion between the components of the two belt ends being joined together in the splices. The goal is to develop adhesion in the splices equal to that in the original belt. There is no intent to physically join the components in the splice, such as stitching together the ends of the fabric plies or joining steel cables with strength-retaining sleeves, etc. The splice lengths, configuration and dimensions are designed to retain continuity of the strength of the belts by the transfer of the tension stresses from one belt end to the other through the adhesion developed between the components mated in the splices.

There are many types of vulcanized splices. Each involves unique procedures, and the materials required depend on the type of belt and the type of vulcanized splice. In the following sections, the more common of the types of vulcanized splices are briefly described along with the types of belt each is used in. No attempt is made herein to provide step-by-step procedures as these vary among belt manufacturers, types of belts, service conditions, etc. The materials required for vulcanized splicing often are unique and specific for the type of belt involved. The procedures and materials or material recommendations must be obtained from the belt manufacturers or their authorized agents.

The term 'vulcanized' may imply a process wherein new materials are used which undergo a chemical change or chemical action as a result of the application of heat and pressure. However, there are commonly used 'cold' vulcanizing processes for rubber belts in which the new splice materials are chemically activated by contact with other chemically active materials, without requiring the use of a vulcanizing press. In general, the splice geometry is the same for hot and cold vulcanized splices, but the materials differ, of course. Materials and procedures for cold vulcanizing usually must be obtained from the cold vulcanizing material manufacturers or their authorized agents, and seldom from the belt manufacturers. In general, cold vulcanized splices can be used in any rubber belt that is step, butt, or overlap spliced, as described in the following sections, but ignoring the references to curing in vulcanizing presses.

Even though this section is titled Vulcanized Splices, the term 'vulcanized' is not correct for thermoplastic belt splices. In thermoplastic belt splices, no chemical change occurs in the materials used. Rather, the thermoplastic materials soften when heated and fuse together with softened material from adjoining components, and then solidify back to their original condition when cooled. Perhaps a better title for this section might be 'Vulcanized or Fused Splices' to reflect thermoplastic as well as rubber belts.

Stepped Splice
Where Used: Multiple ply rubber belts, including rubber type multiple ply lightweight belts, and multiple ply thermoplastic belts.

This splice involves stepping down, ply by ply, the two belt ends to be joined. The dimensions such as step length, cover fill in length, splice angle, etc. will vary depending on the belt ratings and manufacturer. After stepping down, the splice areas are cleaned and buffed to remove irregularities, but without buffing into the fabric surfaces. Thermoplastic belts usually are not buffed. The splices are built up using cements and uncured rubber, or in thermoplastic belts, foils. Accurately fitted splice steps and splice straightness are very important. Assembled rubber belt splices are cured in portable electric vulcanizers, usually with edge irons, and if the belt covers are worn unevenly, with a curing pad. Assembled thermoplastic belt splices are fused using heated plates.

Some high tension two ply rubber belts require the use of special splicing fabric to reinforce the splices. These components must be obtained from the respective belt manufacturers, and must be used exactly as directed to function properly. The splicing fabrics are applied under the cover fill ins in the splices.

Cover fill ins may not be used in vulcanized splices in lightweight multiply belts, either rubber or thermoplastic. Rather, in rubber belts, the covers in the two belt ends are fitted together much like a splice step, with only a bead of new rubber at the seam, or with one cover beveled with an undercut. In thermoplastic belts, the covers in the two belt ends are simply butted at the outside ply seams, with no special bevel cutting. Cover fill ins are not always used in cold vulcanized splices. Rather, the covers in the two belt ends are butted, both having been beveled, one with an undercut.

Butt Splice
Where Used: Single ply rubber belts.

This type of splice involves cutting the two belt ends to be joined at a matching bias angle. The belt covers are removed in the splice area. The resulting surfaces are cleaned and buffed. Before assembling the splices, the belt ends must be aligned and clamped down accordingly. The splices are built up using cement, splicing rubber, splicing fabrics and cover rubber. The splice fabrics must be obtained from the manufacturer of the belt involved, and must be applied exactly as directed. The splices are cured in electric vulcanizers, preferably in a single heat.

Overlap Splice
Where Used: Single ply rubber belts with thin covers and some Aramid belts.

The overlap splice is used in single ply rubber belts with covers too thin to accommodate splicing fabrics. The ends to be joined are cut at a matching bias angle. The splice configuration normally has the leading belt end over the trailing belt end in the splice area unless the conveyor is a decline unit with a tail holdback. The bottom cover of the leading end and the top cover of the trailing end are removed in the splice area. The reverse would apply for the decline type unit described above. After the covers are removed, the splice areas are cleaned and buffed. Cement and splice rubber are applied, and the leading end is laid over the trailing end, with the belts clamped off and aligned. This yields a splice with the two belt ends exposed. These, and the adjacent belt surfaces, must be buffed, and the notches filled with uncured cover rubber. The assembled splice will be thicker than the original belt, with an abrupt offset at the belt ends in the splice. Curing pads are required to fill the offsets. These splices should be cured in electric vulcanizers large enough to do this in a single heat. The curing time should be based on the splice thickness, not the thickness of the original belt.

Finger Splice
Where Used: Single ply thermoplastic belts and some lightweight single ply rubber belts without covers or with thin covers. Sometimes used in multiple ply thermoplastic belts when the pulleys are very small.

This type of splice is commonly used in single ply belts that have thin covers that cannot be stripped off, or have no covers. It is the most common non-mechanical splice method for single ply thermoplastic belts. The overlap type splice is not acceptable in these belts either because of its extra thickness or inapplicability. The method then is to cut matching pointed, triangular shaped, fingers. This is done by several methods, including a template, adhesive backed pattern paper, a cutting die and hand layout. The finger patterns may be 90 degree transverse or at a bias angle. Thin belts can be cut with the ends overlapped, ensuring a match. It is important that the edge fingers be on the leading belt end. The splice is made by intermeshing the fingers of the two belt ends, usually with a layer of thermoplastic film or foil on one or both sides, and in some cases with an adhesive poured into the seams between the fingers. The splice is then heated between electric plates under some pressure to flow the thermoplastic material into the finger seams and fuse it together between the mating surfaces. The splices must be cooled before removing the heating plates to allow the softened thermoplastic materials to solidify.

A variation of the finger splice in multiple ply thermoplastic belts is the overlap finger splice. The fingers are split between belt plies so that in the splice the fingers from the two belt ends overlap each other. Special equipment is required for cutting and stripping out the fingers for this type of splice.

Skived Splice
Where Used: Thermoplastic lightweight belts, single and multiple ply, and nylon core transmission belts.

This type of splice can only be made with special skiving tools. It involves skiving each belt end at a very gentle angle, then overlapping the two skived ends with a layer of thermoplastic material between, and heating the splice area in a portable vulcanizer under pressure. The splices may be 90 degrees transverse or at a bias angle. They should be made with the bottom seam leading. The splices must be cooled before removing from the vulcanizer.

Steel Cable Belt Splices
Where Used: Steel cable belts.

Splices in steel cable belts involve basically removing everything except the cables, with a skin of rubber left on them, from the splice area, and then replacing all of the removed materials with new uncured components. The cables are arrayed in the splice area either in an overlapped pattern, a combination overlapped and butted pattern or exclusively a butted pattern. The choice depends on the amount of space between cables in the original belts, and the cable size. The splices are always made on a bias angle. They are cured in portable vulcanizers large enough to cure entire splices in one heat. The splices must be made and cured with the belt ends accurately aligned. This applies to all splices, but is especially important with steel cable belts since they don't stretch as much as other belts, and thus are less forgiving of crookedness.

Aramid Belt Splices
Where Used: Aramid reinforced high tension one and two-ply rubber belts.

Most Aramid rubber conveyor belts are vulcanize-spliced with a finger type splice as shown in Illustration No. 6. A few are spliced with the overlap type splice described in an earlier section. This description applies only to the finger type splice. In general, the best manufacturers insist that all splice jobs for Aramid belts be referred to them for specific instructions and proper materials. The normal procedure involves stripping the belt ends down to the Aramid ply(plies) top and bottom, then cutting long narrow fingers in the Aramid carcass, and then rebuilding the splice area with tie gum, breaker, or reinforcing fabric and cover rubber. The fingers are interlaced but not touching, with a rubber strip separating them. The splices usually are made 90 degree transverse but can be made on an angle. They are cured in vulcanizers large enough to cure entire splices in one heat. As with steel cable belts, it is especially important that the two belt ends are aligned accurately as Aramid belts are high modulus and thus don't stretch much to forgive crooked splices.

suede · 发表于 2010-2-3 09:59:26

很好的文章啊，我有个关于接头的录像，方法基本一致啊。

kennygu · 发表于 2010-2-3 11:01:51

能给个录像我吗？？我关心指型接法

fenner · 发表于 2010-2-5 14:23:14

你可以和肖爱（天津）联系，他们应该可以给你指尖法和传统接头法的一些介绍；我们也有录像，但由于保密原因，不能公开；他们的介绍比较简单，但从了解角度，足够了；我在北京展览会看过他们放的幻灯片。

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Vulcanized Conveyor Belt Splices

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