ISR is publishing his work in three parts: No linkhandler TypoScript configuration found for key tx_news.., Part 2 in this edition and Part 3 in ISR 5/2016.
3 Factors which influence the long splice
The following section first lists those factors which have a significant influence on the correct functioning of a splice, including an assessment of the importance of that influence.
The additional factors which significantly influence service life are then listed separately below, and their importance is also assessed.
3.1 Some basic principles regarding the correct functioning of a long splice
In order to evaluate a splice and its functionality, it is first necessary to list all the factors which influence the splice.
The question of whether relevant regulations already exist and how strongly the respective factor influences the correct functioning of a splice will be discussed subsequently as a second step.
The following list is intended to show this in general form (Table 1). It must be emphasized, however, that the assessment which follows is the result of personal knowledge and experience, and so the factors could potentially be assessed somewhat differently by other persons.
Answer to question 1 from section 1 (see ISR 1/2016): Which factors influence the correct functioning of a long splice?
It should be clear from the long list that a splice such as is used in modern ropeways is subject to very many complex influencing factors. This also shows that it is very difficult and requires a commensurate level of experience to compare the splicing systems used by various manufacturers with each other.
3.2 Individual assessment of the influencing variables rated as high in respect of the correct functioning of a splice
Answer to question 2 from section 1 (see ISR 1/2016): Are the currently applicable regulations / standards / certification systems adequate to govern safe splice connections?
The regulations currently in effect for Europe are sufficient for the execution of a safe functional splice which complies with the basic requirements for safe operation. They lay down the respective specifications relating to the minimum overall length of a long splice as well as the permissible tensile strength limits (Smin and Smax) in the rope, also relating to facility-specific parameters such as rope sheave diameter, etc.
It should also be mentioned that frequent visual inspections are necessary and meaningful to ensure the functionality of the long splice over the course of its service life and to evaluate its respective current condition.
Because a splice is a safety component, the certification required for placing the splice system on the market is an important additional point.
3.2.2 Facility-specific influencing variables
With respect to the facility-specific influencing variables, the applicable EU standards provide a suitably structured framework. If, as facilities grow ever larger, longer and more extreme, a facility exceeds certain specifications regarding what is permissible with the respective declared deviations from the standards, these deviations must be met with targeted measures. For example, if the maximum permissible safety factor of 20 is exceeded, the basic requirements for safety could be attained once again by lengthening the splice and the tail lengths. Things quickly become more complex when several influencing variables all deviate at the same time.
3.2.3 Rope-specific influencing variables for the rope
Lay length: The selection of rope lay length has a direct effect on the wrapping tension normally applied to the tucked tails. However, because rope lay length does not only affect this parameter, the rope lay lengths of today’s ropeway ropes often lie in the range of a lay length factor of approx. 6.5 to 7.5 x d. This means that for a 50 mm haul rope, for example, the effective rope lay length should be in the range of 325 - 375 mm.
Strand height: With respect to strand height due to preforming, the effective measured strand height must always be less than that which results in the finished rope. How much smaller is a matter for the respective rope manufacturer to decide. This ensures that the respective internal lateral forces are already applied to the tucked tails even when the rope is only lightly tautened and that no strand chafing is possible.
Bending stiffness / strand design: As ropes have continued to increase in thickness, strand design has also changed. Today’s 60 mm ropes have a Warrington-Seale construction whereas earlier ropes in the under 30 mm range were made with a standard or Seale construction. It can be said that an increase in bending stiffness of the strands or the individual wires tends to hinder the development of the necessary wrapping tension.
3.2.4 Specific influencing variables for the wrapping material
Every rope manufacturer and every company that splices ropes uses their own specific wrapping material. The tucked tails are wrapped with this material to ensure a corresponding frictional value between the strands and the tucked tails as well to provide the necessary thickness of the tucked tails.
The respective wrapping material must be very durable and able to endure continuous loading because a rope, and consequently the splice, in a ropeway is subjected to repetitive loading forces, such as flexion, changing tensile forces, torsion and twisting, etc.
3.2.5 External influences
It is a well known fact that ropeways are operated in both the tropics (humidity and heat) and arctic regions (cold, ice, etc.). This means that the splice material required must be resistant to the environmental influences it will encounter, such as UV light, acid rain, heat, cold, dryness etc.
3.2.6 Final observations regarding the factors which influence correct functioning
It must be emphasized that a splice is always an overall system and must therefore be evaluated by every company that fabricates splices according to its specific characteristics and must be certified as an overall system.
Only with this individualized certification procedure and on the basis of many years of experience is it possible to designate a splice system as safe and suitable for use in ropeways.
3.3 Some basic principles regarding service life optimization for a long splice
Just because a long splice functions properly in no way ensures that it is also capable of achieving a long service life. Because this factor is of increasing importance for urban facilities and in general to ensure that the rope’s service life can be utilized to the full, an optimized splice system, many years of experience and test data are of great importance. Table 2 summarizes the influencing factors for the service life of a long splice.
Answer to question 3 from section 1 (see ISR 1/2016): Which factors influence the service life of a long splice?
Long service life in a splice cannot be attained with standard specifications or rigid regulations. Instead, it requires a targeted continuous investment in the materials required for the fabrication of splices, in training for splicers and also in the individualized and application-specific design of splices for high-performance facilities. All these inputs must be based on many years of experience, specific testing and analysis and especially on a desire to constantly improve quality.
Answer to question 4 from section 1 (see ISR 1/2016): Will it be necessary in the future to design and calculate long splices for specific applications or facilities?
The route that is already being taken, entailing the individualized design of splices as in the example of a splice with a maximum safety factor (minimum breaking force / minimum rope force) > 15, should continue to be the direction in which this issue moves. This should be the case for every individual splice system even if only in the interest of the manufacturer.
3.4 Individual assessment of the influencing variables rated as high in respect of the service life of a splice
To our knowledge, there is nothing specific relating to service life in the applicable regulations. Of course, the obligation to exercise diligence applies quite apart from this. For example, a splice should achieve a certain minimum service life, and monitoring by means of the prescribed periodic visual inspections should be ensured.
3.4.2 Facility-specific influencing variables
Here, two separate topics must be examined in more detail. Of course, first of all, negative facility-specific influences such as skewed running, torsion, vibration, unsuitable groove shape, missing insert pieces, etc. must be avoided or reduced to the greatest extent possible. If negative influences such as these are present in great measure, a splice can suffer a good deal and be prevented from reaching its customary full service life.
Furthermore, when there are deviations, it is important to clearly declare them, to evaluate them and to compensate for them with the help of suitable measures. Caution must be exercised in the event that more than one simultaneous deviation makes evaluation and compensation a very difficult undertaking.
3.4.3 Rope-specific influencing variables for the rope
The specifications of the rope manufacturer (sheave spacing, minimum breaking force, rope weight, etc.) and in-house specifications based on experience broadly define the design of the rope (construction, lay length, etc.). Therefore, it is somewhat unusual for rope-specific parameters to be modified only because of a modification in the execution of the splice.
3.4.4 Specific influencing variables for the splicing material
In this specific area, many factors can be identified and optimized which influence the service life of a long splice. Starting with the wrapping material used for the tucked tails, optimized insert pieces and initial and field lubrication of the knots, etc., many points can be found which can be optimized. This is the area in which the compression present in the knot and also in the region of the tucked tails can be reduced, thereby reducing any possible fretting corrosion which may arise in operation. These aspects in turn increase the quality of the individual splice system.
The individual responsibility of all specialist companies begins here as they seek to ensure the high quality and long service life of long splices.
3.6.5 Fabrication-specific influencing variables
Specification of the individual parameters of a splice including the length of the tucked tails, etc. can be used to optimize the quality and the service life of the splice system. The competence of trained and instructed splicers is also essential for limiting quality variances and for the further development of a type of splice. This point is of enormous importance because the work is entirely handcrafted. Moreover, enough time and sufficient manpower must always be made available for a good splice.
A closer look at the issue of optimum service life for a splice reveals some differences or even contradictions in the specifications or requirements found in standards or specified by ropeway manufacturers. For example, the increasing restrictions placed on maximum knot diameter in relation to the nominal or actual rope diameter run contrary to the need to optimize service life. An open discussion of this point is called for in the interest of a splice with good longevity and in order to achieve a meaningful compromise.
3.4.6 External Influences
The type and nature of external influences are well known from thousands of ropeway installations and must be met by using proven splice materials and tested, individual splice systems.
3.4.7 Final observations regarding the factors which influence service life
Splice material and splice fabrication are the most significant factors with regard to service life. Consequently, it is important to continually optimize each individual system for future applications and to find a consensus with the ropeway manufacturer and/or owner/operator with respect to the limit parameters, the time which is made available and the intervals to be scheduled for maintenance work.
Part 3 of "The long splice in ropeway ropes" will appear in ISR 5/2016.