Method of and system for manufacturing a wax impregnated rope and a wax impregnated rope

Ropes made of plastic filaments are used extensively for fishing equipment such as nets and trawl bags, and it has been found that a wax impregnation of the ropes is advantageous in several respects. However, the presence of free wax on the rope surface is undesirable, and according to the invention this is avoided by moving the rope through an impregnation unit (1) comprising a warm wax bath, in such a controlled manner that the rope is only partially saturated, whereafter the rope is air heated at a temperature higher than the melting point of the wax in order for the free surface wax to penetrate into the rope surface.

The present invention relates to a method of manufacturing wax impregnated 
rope. 
In particular for fishing equipment such as nets and trawl bags and the 
like it is desirable that the ropes used for the forming or binding of 
these objects are as ductile and handy as possible and very important that 
they maintain their strength and dimension during long time of use. The 
ropes for this purpose are normally made from artificial material, mostly 
of Nylon. 
For preserving the strength and the knot stability of a rope and for making 
it wear resistant it is known to effect a wax treatment thereof in 
connection with the rope production. This also has the purpose to make the 
rope more ductile and handy. 
Another purpose of such a treatment is to prevent that the rope, when used 
in water e.g. for fishing, takes up water and thus becomes heavier and 
more difficult to handle, while also its tensile strength decreases. 
Moreover, a wax treatment of the rope may prevent sand particles from 
entering the rope, where the sand, in use, may wear on the filaments of 
the rope such that the strength of the rope is reduced, resulting in 
rupture hazards with potential, very serious consequences. Also, the wax 
treatment will reduce the internal friction in the rope as the filaments 
can more easily slide on each other when the rope is stretched, slackened 
or bent. 
Thus, for an efficient treatment of the rope it is desirable to achieve an 
impregnation, whereby the wax is deposited between and around the 
filaments of the rope. It is a possibility to arrange a current waxing of 
the filaments or strands of which the rope is made, as these may be guided 
briefly through a bath with warm, liquid wax. This may result in a fine 
impregnation, but normally the method will imply noticeable difficulties 
in the rope production, where unconvenient wax deposits are liable to 
occur at critical places of the machinery, while also the generally wax 
greasy filaments are difficult to handle in the production of the rope. 
It has been found more suitable, therefore, that it is the finished rope 
that is subjected to the impregnation treatment. In this connection, the 
rope should not only be surface treated, but deep impregnated, and 
according to GB 1,296,339 it has even been suggested to make use of a real 
pressure impregnation, inasfar as it is proposed that a multi core cable 
to be correspondingly treated is moved through a treating chamber to which 
an impregnation agent is supplied under pressure. In connection with rope, 
however, it has not been found necessary to use such a method, because a 
sufficient wax intrusion may be achieved solely by passing the rope 
through a wax bath through a suitable distance or duration. 
In both cases, however, there will be left a noticeable wax coating on the 
outer surface of the rope. It is attractive that the rope be feelable as 
being `wax impregnated`, but this is soon turned into a drawback if a real 
wax layer is exposed on the surface, even if the layer is very thin. It is 
possible to minimize the thickness of the layer by subjecting the rope to 
a scraping or by squeezing it between opposed clamping rollers, already 
for reducing the wax consumption, but is has been found that even hereby 
it is difficult to avoid the non-desired greasy character of the rope as 
caused by even the slightest occurrence of free wax on the surface. 
It should be considered that the wax is left in a natural condition, i.e. 
in a solidified, semi rigid state by the cooling after the rope passage 
through the warm wax bath, without any kind of further fixation of curing. 
It is known to use other, environmentally and operatively less attractive 
impregnation agents, which may be subjected to real curing, cf. U.S. Pat. 
No. 3,424,608 and U.S. Pat. No. 3,911,785, e.g. by a subsequent passage of 
the impregnated rope through a heating zone. Hereby, of course, even a 
remaining outer layer of the impregnation agent may be caused to become 
non-sticky or non-greasy, but this has no bearing on the present 
invention, which is concentrated on the use of environmentally clean and 
non-able, pure wax as the impregnation agent. 
By extensive tests in connection with the invention it has been found that 
in fact it is possible to obtain a rope surface which, after the passage 
of the rope through a warm wax bath, is entirely free of surplus wax, viz. 
in that the rope before or for that sake after a cooling following its 
passage through the warm wax bath is moved through a heating zone for 
heating of the impregnation wax to above its melting temperature. This 
treatment will have nothing to do with a curing of the impregnation agent, 
but to the contrary with a fluidization thereof, such that by an existing 
capillary action the wax will draw inwardly in the rope, partly for 
completion of the interior impregnation and partly for removal of surplus 
wax from the outer surface. It has been found possible to hereby achieve 
an ideal result with respect to the surface being liberated for free wax, 
yet maintaining its character of being wax impregnated. 
Hereby the said operative advantages are achievable while the rope appears 
non-greasy and is suitable for stable knot binding in connection with 
fishing nets, trawl bags and the like. 
It is important to notice that the running-through impregnation of the rope 
should be controlled in such a manner that the rope is not fully 
impregnated, as there will not otherwise be the required capacity for the 
take up of the surplus wax on the exterior surface. 
Moreover, it is important to note that the application of the warm wax with 
its associated intensive heating of the rope filaments will present a 
problem which is already known in connection with any heating treatment of 
ropes: A heating is or may be highly desirable in order to produce a 
precrimping of the ropes, such that it will thereafter be resistant to 
such a crimping which would otherwise, inevitably, occur in practical use 
of the rope as a result of relaxation of internal stresses originating 
from the production of the filaments and/or the rope making. For some uses 
or products, e.g. for trawl bags, it is important that the rope used for 
making the product is generally pre-crimped i.e., pre-shrunk so as to show 
a very low residual crimpability when taken in use, because further uneven 
crimping, e.g. up to an extent of 10% may result in disadvantageous 
wrynesses of the product. The other side of the problem is that any 
heating of the virgin rope will inevitably result in a reduction of the 
strength of the rope, the more the higher the temperature goes. 
For any rope product, therefore, it should be considered whether the 
strength or the residual crimpability has the first priority for the 
intended use. In connection with the present invention it has been found 
possible to aim at both a very low residual crimpability (i.e., degree to 
which it will shrink further) of only 0-1.5% and a relatively low strength 
reduction, while this value is normally higher for effectively precrimped 
ropes. 
For these combined reasons it is important that the rope should be in 
contact with the warm wax bath for seconds only, e.g. less than 10 seconds 
or even for less than one second, while the following heating in air may 
extend over e.g. 5-30 minutes in order to achieve the desirable wax 
distribution without seriously further reducing the rope strength. 
Thus, it is rather critical to adjust the resident time of the rope in the 
wax bath in accordance with the desired properties of the final rope 
product, and in general this will be a matter of empirical adjustment of 
the process parameters. 
The degree of wax absorption and crimping can be controlled by the 
temperatures of the wax bath and the heating zone, respectively, as well 
as by the associated duration of the rope passage therethrough. The 
dimension of the rope is important, as a thick rope may well require twice 
the treating time in the heating zone compared with a thin rope. 
A preferred wax is of the type known as micro crystalline wax, having a 
melting point of about 75.degree. C. The temperature of the wax bath may 
be some 80-100.degree. C. or more, and normally it will be sufficient to 
arrange for the rope to dip through the bath rather briefly, e.g. during 
some 2 seconds. Thereafter, when surplus wax has been squeezed off, the 
rope should continue into a heating unit with an air temperature of e.g. 
120-130.degree. C., ranging preferably between 100 and 150.degree. C. The 
residence time of the rope in the heating unit is comparatively long, e.g. 
some 10 minutes, ranging generally between some 5 and 20 minutes or more. 
This does not mean that the rope should be moved particularly slowly, 
inasfar as it may be present at great length in the heating unit. In this 
unit the rope should be guided such that it is free to undergo the said 
shrinking to the desired extent. 
Preferably, after the heating unit the rope should be subjected to some 
cooling, sufficient to make the wax solidify before a following coiling of 
the rope, as it may then be coiled without sticking problems. 
As mentioned, the preferred wax has a melting point of about 75.degree. C., 
whereby it is taken into account that the wax impregnation can be 
resistant to sun heating, without the turns of a rope coil left in the sun 
sticking together by subsequent cooling. However, the invention is not 
limited to the use of wax with any particular melting point and thus not 
either to any particular temperature range of the wax bath. The bath 
should be at least a few degrees warmer than the melting point of the 
applied wax, but with a relatively cool bath the dripping time should be 
increased again without specific limits. On the other hand the bath 
temperature should of course not be hither than the degeneration 
temperature of the wax or so high as to cause damage to the rope. 
Correspondingly, it is difficult to indicate specific limits for the 
dipping time and the duration and temperature of the air heating of the 
rope. At an elevated air temperature the desired `retraction` of the 
surface wax into the rope might be effected in half a minute, but a longer 
treating time is preferred anyway, also for achieving the desired 
shrinkage of the rope. At a relatively low heating temperature the rope 
will be treated more gently, but then a heating time of e.g. 90 minutes 
may be desirable. 
The rope itself, when properly treated, exhibits a remarkable character in 
that even when unravelled there is no visible deposit of wax, not either 
on the single strands or filaments. There is a small amount of adhesion or 
rather `packing together` between the finest filaments, but not between 
the strands, so the rope is well suited for easy splicing. Thus, it is 
apparent that the wax has really been drawn off from the surface of the 
strands, even where these touch one another, yet leaving the surface 
"impregnated from the inside". The surface is less glossy than normally 
for ropes of Nylon or the like, and it can be touched with a pleasant soft 
feeling ("soft hand"). In use, the smooth and compact surface will account 
for a low water resistance when the rope products are dragged through the 
water, and the rope will maintain its dimensions, with insignificant 
residual crimping (0-1.5%) and without swelling or otherwise increase its 
thickness.

According to FIG. 1, a rope 4 made by a conventional production system (not 
shown) is guided by guiding means 5 first through an impregnation module 
1, then through a heating cabinet module 2 and finally through a cooler 
cabinet module 3, whereafter the rope is coiled in a non-illustrated 
coiling station. In each of the modules 1,2 and 3 and if required even 
between them the rope is guided and advanced by guiding means 5 made as 
wheels or cylinders. Some of them may be driving. The rate of advance can 
be controlled by a control unit (not shown). 
In FIG. 2 the impregnation module 1 is shown in more detail. A rope 4 
enters the module in a mainly horizontal direction as shown by the arrow 
A, via a guiding means 5, whereafter the rope changes direction to 
substantially vertical and is moved down into an impregnation section 6 
holding a wax bath 8. In this bath the rope is guided by two guiding 
rollers 7 which are displaceable horizontally and vertically, whereby the 
submerged length of the rope can be adjusted. The rope 4 moves 
substantially horizontally between the rollers 7 and leaves the wax bath 8 
and the unit 6 upwardly, whereafter it passes through a unit 9 for removal 
of surplus wax, if any, on the rope. This unit consists of two squeezing 
rollers 10 at opposed sides of the rope 4. The rollers 10 are pressed 
together with a force which is adjustable according to the amount of wax 
to be squeezed out of the rope. Thereafter the rope 4 leaves the 
impregnation module 1. 
The heating cabinet module 2, FIG. 3, receives the rope 4 into a closed, 
insulated chamber 11 which is heated to between 80 and 160.degree. C. 
Inside this chamber 11 the rope is guided by a plurality of guiding 
members 5. The air is kept in constant motion by suitable agitation means, 
as indicated by arrows 12. Hereby a more even heat distribution in the 
rope 4 is obtainable. 
In the cabinet 11 the rope is guided through a plurality of loops, e.g. 
20-30 loops, whereby a cabinet of a reasonable size may hold a noticeable 
length of rope, e.g. 50-100 m. The guiding means, e.g. comprising 
individually rotatable carrier pulleys, should be adapted so as to allow 
for the relevant shrinkage (crimping) of the rope, preferably amounting to 
some 8-15% and implying that the roap speed is somewhat lower at the 
outlet than at the inlet. The inlet speed may be of the magnitude 5-25 
meters per minute. 
From the heating unit 2 the rope continues to the cooling unit 3 which, as 
shown in FIG. 4, may be practically identical with the unit 2, except for 
its cabinet 14 being held cooled at some 0-30.degree. C. in order to make 
the warm wax solidify. Also here, it is preferred to make use of air 
circulation as shown at 13. 
As mentioned, a correct treatment of any new rope product will have to be 
empirically based, taking into account the desired properties with respect 
to shrinkage and strength. On the other hand, once suitable processing 
parameters have been ascertained, such parameters will then be reusable 
for achieving fully reproduceable results as long as the particular rope 
product is not changed. 
The following two comparative examples may be illustrating: 
EXAMPLES 
Two three strand Nylon ropes with diameters 11 and 16 m, respectively, are 
subjected to an impregnation treatment according to the invention. The 
following parameters are chosen: 
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Rope diameter 11 mm 16 mm 
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Speed through wax bath 
15 m/min 9 m/min 
Submerged rope length 
200 mm 250 mm 
Bath temperature 100.degree. C. 
100.degree. C. 
Residence time in bath 
0.8 sec. 1.7 sec 
Rope length in heater unit 
80 m 80 m 
Temperature of heater unit 
120.degree. C. 
125.degree. C. 
Residence time in heater unit 
5.3 min 8.8 min 
Rope length in cooler unit 
80 m 80 m 
Temperature in cooler unit 
23.degree. C. 
23.degree. C. 
Crimping 10-13% 
Weight increase 5% 
Strength reduction 10% 
Residual crimping 0.5% 
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