Image 1: Working on a long splice
Technology

The long splice in ropeway ropes – Part 1

During the 5th International Stuttgart Rope Days, which were held in parallel with the 2015 OIPEEC Conference last March, Bruno Longatti, Technical Director of the Swiss ropeway manufacturer Fatzer AG, presented an impressive paper on the state of the art and science with regard to the long splice in ropeway ropes.

Created by Bruno LONGATTI - Fatzer AG

ISR is presenting the paper in three parts (in this and the next two editions), in which the author gives an overview of this essential method of joining ropes, reports on experiences with the geometry of the splice and treats the influence of the splice on rope life.

1 Introduction 

Splicing is a very old means of joining ropes and even today is still the only method of rope joining which creates an endless loop. For quite some time now, the lengths of the tucked tails in a long splice as well as the overall length of the splice have been standardized so that the functionality of a rope splice can be ensured. 

The specifications contained in the applicable standards have been defined primarily with respect to the requirements that arise under the typical operating conditions found in ropeways, which must ensure safe and proper functioning and that the rope connection can never slip apart. 

These must also include the requirement that a long splice must not produce a noticeable thickening of the rope due to the detachable clamps that are used. It is also important to ensure that a suitable service life is achieved for these connections. The more frequently spliced endless-loop ropes are used in urban installations, the more importance must be attached to the achievable and implementable service life. 

Various existing, older studies (Overlach 1931) have treated the aspect of adequate length of the tucked tails as well as the necessity of preventing bulge formation and the reduction of the radial forces or holding forces on the tucked tails. It is not an objective of this paper to reexamine the good quality work or to expand it to account for the situation faced today (thicker ropes with multi-layered stranded designs). Instead, the paper focuses on identifying and evaluating the most important points that are of greatest significance for achieving a desirable service life. 

When we consider the current specifications for splicing, the total length of a long splice has remained about the same over the last 80 years at ≥ 1200 x d (d = nominal rope • in mm). In contrast, however, the tucked tails have tended to become shorter in some countries. In consequence, the current minimum length of the tucked tails is 60 x d according to the harmonized specifications of EN standards. In fact, in earlier times in the USA, the applicable regulations called only for a minimum of 30 x d. Before 2003 in Switzerland, a limit value of 50 x d was called for as the minimum length for the tucked tails. Based on experience with these values, as some splices of these types are still in service, it can be shown that the current standard specifications function well under normal conditions when applied in appropriate splicing systems. 

Furthermore, it must be borne in mind that the manner in which a long splice is fabricated varies depending on the manufacturer making the splice, the different wrapping materials for the tucked tails as well as the manner in which the splice is executed (tucked tail length, knot type, type of twisting, etc.). It is essential that these important aspects be considered in the design of a long splice, which makes it impossible to make generalized evaluations without specific knowledge of the splicing system. 

When the long splice is considered in terms of service life, a factor that is continually growing in importance in urban installations, then special attention must be given to the knot or the region of the tuck tail ends. These are the primary areas that experience the fatigue that limits service life. 

Consequently, a number of questions arise which are essential for the design of a long splice that offers proper function and economy but also long service life. 

  • What factors influence the proper function of a long splice?  
  • Are the currently applicable regulations / standards / certification systems  adequate to govern safe splice connections?  
  • What factors influence the service life of a long splice?  
  • Will it be necessary in the future to design and calculate long splices for  specific applications or facilities?  
  • Where do the limits really lie with respect to the length of the tucked tails as well as the overall length of a long splice?  

In the following sections, an attempt will be made to provide information and facts to answer these questions. 

1.1 The history of ropes and the long splice 

The term “splicing” means joining two ropes together. 

The history of ropes is truly impressive. Even today, most ropes still have a structure similar to that used more than 2,000 years ago. 

Ropes continue to play an important part in many typical situations of our daily lives. They continue to be an indispensable part of any system in which it is necessary to divert tensile forces via rollers or pulleys. 

Rope makers' guilds existed for centuries and still today, thousands have this trade as a part of their name. Rope makers learned to make ropes using natural and synthetic fibers as well as wire ropes and was able to fabricate them to suit their customers’ needs as well as install and maintain them. Today, however, the number of rope manufacturers is dramatically smaller and most of these are specialists for a very limited range of applications. Consequently, training to become a rope maker is often only possible in the textile industry and only at a very few locations when viewed from a global perspective. It can also be said with certainty that today’s rope maker concentrates primarily on the fabrication of ropes, and the work of splicing is performed by a specialist splicer (image 1). 

Image 2: Short splice with ends whipped

2 Types of Splices

2.1Short splice 

The short splice is used to join two laid ropes (image 2). To do so the ends must be unraveled so the individual strands are separated. They are then braided together using a special technique including tucking, careful tightening and finishing. The number of tucks required depends on the rope material (steel wires, natural or synthetic fibers). 

A disadvantage of the short splice is its thickness, which can impede or prevent clamping or proper passage of the rope through a pulley. Consequently, the short splice cannot be used to join the ends of stranded ropes to create endless loops for ropeways. 

2.2Long splice 

The long splice is also used to join two laid ropes (figure 1) just as the short splice is. In comparison to the short splice, it offers the advantage that there is no appreciable thickening of the rope in the general splice region. There is only a certain thickening in the knot region, where an additional strand must always be included. 

A splice for joining a typical 6-stranded wire rope with a synthetic core has a length of about 1200 x d to 1300 x d (1200 to 1300 times the nominal rope diameter). In practice, this results in a splice with a total length of over 60 m for a 50 mm rope. The splice must be performed on site after the pulling in and reeving and before final placement of the rope that often has a length of several kilometers. Another special aspect is that during the actual splicing, the strands are not laid alternately, but the core itself is removed on both sides over a length of about 50 to 100 x d so that afterward, the respective wrapped strand end, which is of approximately the same thickness, can take its place. 

This permanent means of joining two ropes, the long splice, requires work done by hand. To do this, the respective ends of a rope are unlaid and subsequently braided together. This requires special care. A splice that has been made correctly should always have a higher or similar breaking strength than the actual rope itself. This has also been proven by means of appropriate tests. 

2.3  Current geometric specifications for a long splice 

At present, a long splice (figure 2) in a ropeway haul rope must conform to normative geometric specifications (EN standard): Overall splice length ≥ 1200 x rope •, tucked strand tail length ≥ 60 x rope •.

At present, the knot diameter of a long splice in a ropeway haul rope must conform to normative geometric specifications (EN standard): Diameter ≤ 1.10 x nominal rope •. 

Further important points for an acceptable splice system include:  

  • Circularity of the knot 
  • Suitable knot insert piece which retains its form 
  • As little strand contact as possible 
  • Compliance with the diameter specification that may be further restricted by the ropeway manufacturer (+8 %). 
  • Interlaced cross knot 
  • Suitable insert piece 

Compliance with these points, especially the further important points, has a significant effect on the service life of a splice. It must be emphasized that a knot that is as small as possible may be advantageous for detachability. In terms  of service life, however, a reduction of the diameter leads to a considerable decrease in service life. This has been proven numerous times using our in-house rope test setup and is confirmed through field experience.

2.4 Configuration variants for splices

2.4.1  1+1 splice:

In the 1+1 splice (figure 3), every other strand (e.g. 1+3+5) of one end of the rope and the corresponding strands (e.g. 2+4+6) of the other end of the rope are braided together. This type of splice requires more effort because each strand must be unlaid from the individual rope end separately and then braided into the other rope end. However, this type of splice has significant advantages based on its symmetrical distribution as well as for use in splicing an old and a new rope (repair splice or joining splice) or in the event that the rope characteristics or the strand diameters differ slightly.  

2.4.2  3+3 Splice:  

In a 3+3 splice (see the sketch of a 3+3 splice, figure 4), three strands that are adjacent to one another (e.g. 1...3) at one end of the rope as well as three adjacent strands (e.g. 4...6) plus the associated rope core are twisted together or married. The marrying of the two rope ends to be spliced using this method is considerably simpler and faster.  Because one half of each rope is twisted together, special attention must be given to maintaining the same rope characteristics as well as identical breaking forces when twisting them together. If this point is disregarded, a corresponding asymmetry could arise within the splice which could have a detrimental effect on the quality of the splice during operation.  

2.4.3  Splice with a middle part: 

A middle part is planned for in a splice for one of the following reasons:  

  • The tucked tails in a 6-stranded rope are shorter than 100 x d, which creates a remaining length as compared to the overall length of a splice of 1200 x d. This remaining length (e.g. 1200 d – (2 x 6 x 60 d) = 480 d) is customarily placed in the central section of the splice and is therefore called the middle part. 
  • Right from the start, a remaining length as compared to the overall length of the splice of, for example, 1200 x d is planned for in the central section of the splice. It is then possible to use this remaining length for an initial shortening of the loop. For this shortening, a loop corresponding to the shortened length is first created at the middle of the rope. Then, only those strands which are to be tucked and which face away from the centre of the splice for each knot are unlaid and subsequently placed back in without following the loop again. Using this approach, the initial rope loop disappears after all the strands have been unlaid and then twisted back in according to the procedure described above. This somewhat faster method of shortening results in one knot strand per knot remaining unchanged, which is the reason this method cannot be used for the repair of damaged knot strands. 

There are differences of opinion on the true value or advantage of a middle part. For this reason, there is some justification for dispensing with a middle part. This would allow the overall length of a long splice to be shortened to a minimum of 720 x d in accordance with the currently applicable minimum tucked tail lengths of 60 x d. The corresponding reduction in time and material for fabrication would significantly improve the economy factor, especially for urban installations. 

2.5 Types of knots 

2.5.1  Parallel knot: In a parallel knot (figure 5, left), the two knot strands are laid so they are parallel (see the left side of the figure) as they pass one another before they are inserted into the core of the rope and end as tucked strands. The parallel arrangement of the stands relative to each other in parallel knots means that directly in the knot area there is a certain area where 7 strands are adjacent to one another, thereby causing a significant increase in the rope diameter (up to +15 % greater than the nominal •). This is without subjecting the knot strands to any compression that would be too great or to increased fretting corrosion. Parallel knots, in terms of easy recognition due to the significant knot diameter, are only used very seldom now for permanently clamped ski lifts or chair lifts.  

2.5.2  Cross knot:  

In a cross knot (figure 5, right), the two knot strands are laid so they cross over (see the right side of the figure) in the knot area before they are inserted into the core of the rope and end as tucked strands. Due to the crossed strands, cross knots result in less increase in rope diameter (up to +10 % greater than the nominal •). The cross knot has clearly become the favorite for facilities utilizing endless-loop ropes and detachable clamps.  

2.5.3 Interlaced cross knot: 

In an interlaced cross knot (image 4), the strands to be crossed are unraveled in the knot area and are put back together in an ideal fashion so that the pressure is reduced through a greater contact surface area, and the effective diameter of the two knot strands causes even less increase in the splice knot diameter. 

 

Part 2 of “The long splice in ropeway ropes” will be printed in ISR 2/2016. 


[Translate to English:]

The organizers of MOUNTAIN PLANET, one of the world's leading trade fair for the mountain planning and industry, have decided to cancel the 2020…

Read more

Winter Park is one of Leitner Poma of America’s installation highlights this season and marks the introduction of Leitner Direct Drive technology.

Read more

Since its foundation in 1969, the Swiss family business has grown into a leading one-stop supplier for ticketing, access management and security…

Read more

The Axess RESORT.SOLUTIONS offer smart solutions to manage operations for ski resorts of the future. All-in-one approach reduces administrative…

Read more

NSAA 2019 english

Read more

NEVEPLAST for skiing in Copenhagen

Read more
[Translate to English:] LEITNER ropeways

29 September 2018 marks a historic day for modern ropeway systems. With the opening of the world's highest 3S gondola lift on the Klein Matterhorn,…

Read more

In the past ten years, Alpitec China has successfully established itself as the leading platform for mountain and winter technologies in the…

Read more
[Translate to English:]