CA1112078A - Automatic tension transmission belt - Google Patents
Automatic tension transmission beltInfo
- Publication number
- CA1112078A CA1112078A CA315,747A CA315747A CA1112078A CA 1112078 A CA1112078 A CA 1112078A CA 315747 A CA315747 A CA 315747A CA 1112078 A CA1112078 A CA 1112078A
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- CA
- Canada
- Prior art keywords
- belt
- tension
- polyester fiber
- fiber cords
- shrinkage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
Title of Invention: Automatic tension transmission belt ABSTRACT OF THE DISCLOSURE
An automatic tension transmission belt in which polyester fiber cords are embedded in such a fashion that the belt can meet the condition of A> B where A is the amount of strain at the room temperature and B is the amount of strain at the temperature of 80°C, both in the fixed load.
An automatic tension transmission belt in which polyester fiber cords are embedded in such a fashion that the belt can meet the condition of A> B where A is the amount of strain at the room temperature and B is the amount of strain at the temperature of 80°C, both in the fixed load.
Description
This invention relates to an automatic tension trans-mission belt and, more particularly, to a transmission belt of automatic tensility which shrinks and tenses by the frictional heat generated upon its slipping on a pulley during running, thereby automatically maintaining the tension necessary for transmission.
Friction transmission belts which are used with pulleys generally exhibit, while in use, real belt elon-gation caused by bending, stretching and compressing, and apparent elongation or loosening due to wearing at both sides (in the case of a V-belt) and slippage further into the pulley groove. If such belt elongation takes place, the belt tension is reduced and the belt is incapable of transmitting the prescribed load, with the result that the slippage of the belt during running increases abruptly.
Thus, frictional heat is generated and wear of the belt is accelerated and the belt eventually fails. In order to eliminate such problems, it is necessary to keep the belt in constant tension by regulating the center distance (distance between the centers of two pulleys) or by pro-viding a tensing means, such as a tension pulley, for which extra space is required. Another method of main-taining the belt in tension in general practice is to give the belt, when in place on a pulley, an initial tension which is 30 - 40% higher than the tension normally required for transmitting the prescribed load so that any slackening of the belt tension does not result in slippage. This method, however, has the disadvantages that the service life of the belt is significantly reduced under the pressure of the increased tension, and also the pulley axles may bend or the pulley bearings may wear .~, ~
,, ~ ji. ', : . .
rapidly as a result of the greater load applied to the pulleys.
These days, highly complex meehanisms employing tension belts are generally enclosed easings of the prescribed capacity for automobiles, computers and various other machines. Accordingly, when a transmission belt becomes loose, re-tensioning of the belt requires dis-assembling, replacing and re-assembling of the machine.
This requires much time and labor.
As the following description refers to the accom-panying drawings, all of the drawings will first be introduced for elarity, as follows:
Fig. 1 shows a eross section of a V belt according to one embodiment of the present invention;
Fig. 2 and Fig. 3 show respectively an outline of the testing apparatus for a V belt;
Fig. 4-A and Fig. 4-B show respectively the relation between belt tension and running hours, obtained from the result of running tests in Experiment I and Experiment II
given later; and Fig. 5 to Fig. 8 show respeetively eross seetions of eonventional V belts.
Conventional transmission belts are available in several kinds, sueh as flat belts and V-belts. Fig. 5 to Fig. 7 show eross seetions of eonventiontal V belts, in whieh a is a surfaee eanvas; b is adhesive rubber; e is a polyester fiber eord; dl is eareass fabric; e is bottom rubber; f is a bottom eanvas and d2 is a rubber layer with fibers oriented about 90 to the longitudinal axis of the belt.
If a V belt is used for a ear engine, for example, the initial tension of the belt will be reduced due to its residual strain in proportion to running distance. Causes of such elongation of the belt are roughly divided into:
(1) apparent elongation due to the belt descending further into the groove of a pulley as a result of abrasion at both sides of the belt; (2) real elongation of polyester fiber cords embedded in the V belt; and (3) apparent elon-gation due to the deformation of the cross sectional shape of the belt caused by lateral pressure applied to the sides of the belt during running. The aggregate of these three factors brings about a gradual reduction of tension, with resultant elongation of the belt which causes belt slippage. It has been the usual practice that when elongation of the belt occurred, tensioning of the belt, namely, adjusting of the belt tension, has been carried out.
In order to decrease the requirement for belt re-tensioning, or to dispense with belt re-tensioning altogether, it is necessary to prevent such elongation of the belt. In this respect, it has been suggested to use, as belt reinforcement, polyester fiber cords of such pro-perty that their elongation at 100C and that at 24C are almost equal, for the purpose of minimizing the elongation of the cords (U.S. Patent No. 3,469,001). However, such a belt with polyester fiber cords embedded therein is still stretched on pulleys at a high initial tension (the lowest tension at which no slippage takes place plus 50% or more extra tension) to increase the time required for re-tensioning of the belt. However, as stated above, since the belt is stretched on pulleys at such a high tension, a large load is applied to both the pulley axles and the , ~,. . .
;r ~' "~
bearings, with resultant bending of the axles and wearing of the bearings. Furthermore, the belt is sensitive to shock load because a high factor of safety cannot be provided for the belt as it is anyway over tensioned and therefore trouble at an initial stage will increase.
From the above, it can be seen that a belt in which polyester fiber cords of the above-mentioned type are embedded is improved with respect to the elongation of the cords, but elongation due to other factors remains unimproved and therefore the belt tension will be gradually reduced. On the other hand, if the belt is installed on pulleys at a tension lower than the lowest tension at which belt transmission is possible, belt slippage occurs immediately after the start of belt running and re-tensioning must be carried out. Also, if polyester fiber cords c of very high shrinkage tension are used for the V belt having neither woven fabric dl nor rubber layer d2 shown in Fig. 6, the cords c in the transmission belt will become partially buried in the bottom rubber e as shown in Fig. 8, during the vulcan-izing process and as a result the arrangement of cords will be disordered. In order to prevent this problem, it will bé necessary to increase the viscosity of the bottom rubber e shown in Fig. 8 or to employ a construction as shown in Fig. 5 and Fig. 6. In the typical conventional belt having polyester fiber cords, the cords are made of polyester yarn having the following characteristics.
;i r3 Relative viscosity: 0.60 - 0.70 (dissolved in orthochlorophenol) Tenacity: 7.5 - 8.5g/D
Elongation: 11 - 15%
Heat shrinkage: 5 - 10~ (held for 30 minutes at 150C) Shrinkage tension: 0.2 - 0.4g/D (at 185 - 215C) (maximum tension) In the above characteristic values, g represents gram and D represents the denier of the fiber. The relative viscosity of polyester yarn was obtained in the following way, namely 29 of polyester fiber was dissolved in 25ml orthochlorophenol; the viscosity was then measured by Ostwald's viscosimeter; the measured value was divided by the viscosity of orthochlorophenol, multiplied by 0.024 and then 0.02634 was added. The tenacity and elongation were measured according to JISL-1017-1963 (constant speed stretching type). Hat shrinkage was measured according to JISL-1017-1963.5.12 by maintaining a sample for 30 minutes at 150C. Shrinkage tension was measured according to JISL-1017-1963.5.13 at a temperature ranging from 185C to 215C and the maximum value obtained throughout the whole measurement was made the shrinkage tension.
According to the invention there is provided an auto-matic tension transmission belt having polyester fiber cords embedded therein, characterized in that said poly-ester fiber cords shrink at a temperature of 80C or higher, so that, when the belt is installed between two pulleys for the transmission of force therebetween, the frictional heat generated by any slippage of the belt causes the fiber cords to shrink at the said temperature, thereby increasing the belt tension and eliminating said slippage.
,~
The automatic tension transmission belt according to the present invention uses polyester fiber cords as the core materials. These are preferably made by twisting polyester fiber yarn having a relative viscosity of 0.90 - 1.30 in solution in orthochlorophenol and a maxi-mum shrinkage tension of 0.40 - 0.55g/D at a temperature ranging from 180C to 215C, are subjected to a hot stretching process of more than 5% elongation percentage by multi-stage stretching and are embedded in rubber constituting the belt, while maintaining the proper thermal force of polyester fiber cords during the vul-canizing process of said rubber. While such belt is running, the above-mentioned polyester fiber cords shrink by their thermal contractile force at a frictional heat of higher than 80C generated by belt slipping caused by lowering of belt tension. Thus, the belt tension recovers to the minimum tension necessary for transmission of power, thereby eliminating belt slipping and maintaining its tension at a regular level, with automatic repetition of such re-tensioning if further slipping occurs.
An embodiment of the present invention is explained below, with reference to a V belt. Fig. l shows a cross section of a V belt l according to-the present invention.
Numeral 2a denotes a surface canvas. Numeral 2b denotes a bottom canvas. Numeral 3 denotes adhesive rubber.
Numeral 4 denotes a polyester fiber cord to which a special drafting process has been imparted. Numeral 5 is a bottom rubber.
The above-mentioned polyester fiber cord 4 was made by twisting material yarn having the following characteristics:
, Relative viscosity: 0.90 - 1.30 (dissolved in orthochlorophenol) Tenacity: 8.5 - 9.5g/D
Elongation: 12 - 15~ (elongation at break) Heat shrinkage: 8 - 11% (held for 30 minutes at 150C) Shrinkage tension: 0.4 - 0.55g/D (the maximum tension at 180 - 215C) Where: g = gram D = Denier of fiber The relative viscosity, etc. were measured in the afore-mentioned way.
The above-mentioned cord 4 is subjected to an adhesion treatment and a heat drafting treatment. The adhesives used for the adhesion treatment may be, for example, iso-cyanate type adhesives, epoxy type adhesives, RFL, etc.
The hot stretching process is carried out by a multi-stage stretching at a stretching percentage of more than 5%, preferably the stretching percentage should be increased gradually with the progress of stretching process. Polyester fiber cords 4 to which the hot stretching process has been imparted are embedded in the above-mentioned bottom rubber 5 as tensile members. When vulcanizing the bottom rubber, care should be taken to ensure that the thermal contractibility of the cords 4 is not impaired, for example, rubber vulcanizable at a low temperature may be used as the material for the bottom rubber 5 to increase the viscosity of the bottom rubber 5, or to interpose between the cord 4 and the bottom rubber S
a carcass or a rubber layer with fibers arranged in the direction about 90 to the longitudinal axis of the belt (please refer to Fig. 5 and Fig. 6).
While the V belt of the above-mentioned construction , ~r4,,,~ ~ 7 --is running, belt tension is reduced by generation of apparent elongation, real elongation, abrasion and defor-mation of the cord 4, and when the belt tension decreases below the minimum tension required, belt slippage takes place and the V belt 1 itself generates heat due to fric-tion. When the temperature of the V belt 1 rises above 80C due to such frictional heat, the above-mentioned polyester fiber cords 4 embedded in the V belt 1 shrink as a result of their thermal contractile properties, and if the cords 4 shrink in excess of the belt elongation percentage at which belt slippage took place, the belt recovers the minimum tension necessary for transmission of power and consequently belt slippage is eliminated.
In response to the elimination of belt slippage, the belt temperature is reduced and, accordingly, the cord 4 ceases to shrink.
When the V belt 1 elongates due to its running and belt slippage takes place again, the belt tension is again recovered automatically to the minimum tension necessary for transmission of power and to maintain tension at a regular level. In short, whenever the above-mentioned V
belt 1 elongates, irrespective of the cause of elongation, it shrinks and recovers its tension in response to the elongation.
As mentioned above, in order to enable the V belt 1 to have this automatic tensioning action, it is essential that the polyester fiber cords 4 embedded in the V belt 1 possess very high shrinkage tension. For increasing the shrinkage tension of the cord 4, firstly the material of the polyester fiber yarn itself must have a high relative viscosity (0.90 - 1.30) and a high shrinkage tension (0.40 - 0.55g/D), secondly the hot stretching process 1 ~ A
. .
to be imparted to improve the shrinkage tension of the cord 4 must be based on a multi-stage stretching of more than 5% elongation, and thirdly the shrinkage tension improved by the hot stretching process must not be reduced during the vulcanizing process. If the relative viscosity of the yarn material is increased, its strength, heat shrinkage and shrinkage tension will increase, with resultant improvement of thermal contractile force and temperature-sensitive characateristics. Similarly, the hot stretching process involving multi-stage stretching to more than 5% brings about a higher heat shrinkage and higher shrinkage tension, with the result of higher thermal force and improved temperature-sensitive char-acteristic. Thus, thermal shrinkage occurs immediately in response to an increase of belt temperature upon belt slippage and consequently the required tension is quickly recovered. It must be noted, however, that polyester fibers having a relative viscosity of more than 1.30 are difficult to manufacture.
Tests were carried out to see if the above-mentioned V belt possesses a tension recovering function and to specify such characteristic.
I. Static test (a) Testing apparatus A testing apparatus as shown in Fig. 3 was used. V
belt 1 for testing is put on flat pulleys 8, 9 supported by pulley holders 10, 11 by such a method that their rear sides make contact with the pulleys. These are put in a thermostatic chamber 7. The pulley holder 10 is hung on a load cell 6 and a loading weight 12 is suspended from the pulley holder 11.
- _ g _ , i,~,. ..
(b) Testing method In the following procedure, the above-mentioned V belt 1 is put in a condition closely resembling the condition in which it actually runs, and its characteristics are obtained. The testing procedures 1 - 6 were carried out at room temperature (20 - 25C).
Testing procedure 1 To put the V belt 1 on the pulleys 8, 9, with its rear side in contact with the pulleys.
Testing Procedure 2 (Center distance Xl) To apply a load Wl (1/8 of the tenacity at break) to the V belt 1 and read the center distance Xl in that position. To leave the V belt 1 for 10 minutes as it is and read a load W2 after relaxation of force. The load Wl corresponds to an initial tension at the time when the belt is fitted, in other words, the procedure 2 sets the condition at the initial stage of belt fitting.
Testinq procedure 3 To pull at the stretching speed of lOmm/minute. To apply a load W3 which is one-fifth of the tenacity at break and leave for one minute and then put back to the load W2 at the speed of lOmm/minute and leave for 30 seconds. This operation is repeated three times.
The load W3 corresponds to the transmission tension acting upon the tight side at belt running and the lGad W2 corresponds to the tension on the slack side. In other words, the procedure 3 sets the condition in which each poiint of the belt passes the tight side and the slack side according to the belt running.
Testing procedure 4 (Center distance X2) To pull at the stretching speed of lOmm/minute. To apply a load W3 which is one-fifth of the tenacity at break and leave for one minute and then put back to X2 (position of 0.996 x Xl) at the speed of lOmm/minute and leave for 2 minutes.
The center distance X2 moves the pulley to make the V belt generate an apparent elongation. The movement of the pulley corresponds to the elongation percentage (allowable elongation percentage) by which slip occurs in actual belt running. In other words, the procedure 4 sets the condition in which the V belt elongated due to belt running. The allowable elongation percentage C is { (Xl - X2) /Xl } X 100.
Testing Procedure 5 (Strain A and center distance X3) To pull at the st etching speed of lOmm/minute, apply a load W3, leave for two minutes and read a center distance X3.
Strain A = {(X3 - X2)/Xl} x 100 Strain A is a strain at the room temperature and at the load W3 corresponding to the transmission tension and corresponds to the strain to which the V belt is sub-jected at belt running. The larger the value of strain, the more the belt slipping tends to take place.
Testing Procedure 6 ; To put back to the point X2 at the speed of lOmm/minute and then leave for two minutes.
Testing procedure 7 To blow hot air in a thermostatic chamber 7 in the condition where the load W2 is applied after relaxing of stress and continue to heat at 80C until contractile force is made constant in hot air.
The heating temperature 80C corresponds to the . .
temperature at which heat is generated due to belt slipping, namely, the procedure 7 sets the condition in which the belt slips due to its elongation, generates heat of 80C due to frictional heat and then shrinks.
Testing Procedure 8 To pull up the load W3 at the stretching speed of lOmm/minute and read a center distance X4 at that time.
Strain B = (X4 - X2)/Xl x 100 The strain B is a strain at the temperature of 80C
and at the load W3 corresponding to the transmission tension and corresponds to the strain to which the V belt is subjected when the belt generates heat. The less the value of this strain, the more the belt slipping becomes easy to be removed.
(c) Test results Each load of Wl - W4 and each center distance of Xl - X4, together with Strain A, Strain B obtained from the load and the center distance, and an allowable elongation percentage C are shown below, in comparison between the V belt according to the present invention and the conventional V belt.
`~
~ _ .
.
V belt according to the present Conventional invention V belt Wl 56 kg 56 kg W2 48.5 kg 44.5 kg W3 90 kg 90 kg Xl 413.3mm 415.Omm X2 411.647mm 413.34mm X3 416.069mm 418.237mm X4 413.362mm 417.013mm Strain A 1.07% 1.18%
Strain B 0.415% 0.885%
A - B 0.655% 0.295%
C 0.400% 0.400%
From the above test results, it can be seen that in order to make the V belt possess the automatic tensioning action whereby the belt shrinks upon belt slipping and recovers its tension, it is required that the belt gen-erates contractile force when the temperature lS raised to 80C and the strain B at this 80C is smaller than the strain A at the room temperature. Also, it is required that the difference between the two strains or A - B is larger than the allowable elongation percentage C at the belt slippage, in other words, the belt tension after shrinking due to generation of contractile force should be the tension at the time prior to belt slippage. ~
With regard to the above requirements, both the V belt `
according to the present invention and the conventional V belt satisfy the re~uirement of A , B. However, in respect of the relation between A - B and the allowable -elongation percentage C, while the V belt according to the present invention indicates A - B > C, the conventional V
belt indicates A - B < C. This means that while the V
belt according to the present invention possesses auto-matic tensioning action, the conventional V belt shows thermal shrinkage to some extent but such thermal shrink-age is not sufficient to correct belt slippage. This point has been confirmed by the dynamic test mentioned below.
II. Dynamic test (a) Testing apparatus The testing apparatus shown in Fig. 2 was used. The V
belt 1 was installed on the driving side, the driven side and idle pulleys 13, 14, 15 with the location as shown in Fig. 2, and the running test was carried out with the belt span initial tension set at 30 kg by a belt tension gauge.
The diameter of V-grooved pulleys 13, 14, the diameter of the V-grooved idle pulley 15, the number of revolution of the V-grooved pulley 13 on the driving side and the shaft load on the driven side were 127mm, 76.2mm, 4,700 r.p.m.
and 13 ps respectively. V belt 1 of A-shape No.40 (JIS K 6323) was used.
(b) Test results Test results as shown in Fig. 4-A were obtained. In order to maintain the span tension of 30 kg, the conven-tional V belt must be re-tensioned twice, 0.1 hr. and 0.6 hr. after the start of the running, but V belt according to the present invention does not require such re-- tensioning. In this test, while the V belt according to the present invention retained the original span tension of 30 kg even at the end of 200 hours after the start of ~3~
running, the conventional V belt lowered its tension to the level of 22 kg, in spite of the re-tensioning effected twice at the early stage after the start of running, and continued to lower its tension, with the result of the difficulty of transmitting the prescribed load. Thus, further re-tension was required for the conventional V-belt.
Experiment II
(a) Testing apparatus The same testing apparatus as used in Experiment I
(refer to Fig. 2) was used. The V belt was installed on the driving side, the driven side and idle pulleys 13, 14, 15, with the belt span initial tension set at 10 kg by a belt tension gauge, and the running test was carried out.
The diameter of the V-grooved pulleys 13, 14, the diameter of the idler V-grooved pulley 15, the number of revolution of the V-grooved pulley 13 on the driving side, and the shaft load on the driven side were 127mm, 76.2mm, 4,700 r.p.m. and 13 ps respectively. V belt 1 of A-shape No. 40 (JIS K 6323) was used.
(b) Test results Test results as shown in Fig. 4-B were obtained. As the span tension was set at 10 kg, which was less than the lowest span tension necessary for load transmission, the conventional V belt was broken down in only 0.1 hours after the start of running due to a sudden slip, whereas the belt according to the present invention regained the span tension of 30 kg soon after the start of running and thereafter maintained the span tension of 30 kg. Similarly to the case of Experiment I, since the belt according to the present invention shrinks due to heat generated by 's'~ ' slippage or has an automatic tensing action, it does not require re-tensioning at all and shows recovery of tension by its own automatic tensing action even if its tension was set below the lowest tension necessary for load transmission.
In addition, various test specimens of polyester fiber material yarn were prepared, by varying the rela-tive viscosity (0.7 and 0.9), the stretching process (one-stage stretching at 3% and 5% and two-stage elongation at 5% or more) and the shrinkage percentage of polyester fiber cords before and after the vulcanizating process (0.3 - 1.3%), and each test specimen was tested for the value of shrinkage tension, based on which the value of shrinkage tension was obtained, as shown in Table 1. Also, from the results of the above-mentioned static test and the results of the dynamic test (Experiment I), the existence of automatic tensioning action of each test specimen was obtained, as shown in Table 2.
In these tests, polyester fiber material yarn of 1100 deniers, polyester fiber cords construction of 2 x 5 twist and belt of A-shape No. 40 (I.S.O. Recommendation R608 -Belt length 40 inches) were used. The maximum shrinkage tension is the maximum value at the temperature ranging from 180C to 215C. The shrinkage tension was measured according to the JIS L-1017-1963 (method of measuring the shrinkage tension upon dry heating). The hot stretching process was done at the temperature of 230C and for the exposure time of 120 seconds.
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Friction transmission belts which are used with pulleys generally exhibit, while in use, real belt elon-gation caused by bending, stretching and compressing, and apparent elongation or loosening due to wearing at both sides (in the case of a V-belt) and slippage further into the pulley groove. If such belt elongation takes place, the belt tension is reduced and the belt is incapable of transmitting the prescribed load, with the result that the slippage of the belt during running increases abruptly.
Thus, frictional heat is generated and wear of the belt is accelerated and the belt eventually fails. In order to eliminate such problems, it is necessary to keep the belt in constant tension by regulating the center distance (distance between the centers of two pulleys) or by pro-viding a tensing means, such as a tension pulley, for which extra space is required. Another method of main-taining the belt in tension in general practice is to give the belt, when in place on a pulley, an initial tension which is 30 - 40% higher than the tension normally required for transmitting the prescribed load so that any slackening of the belt tension does not result in slippage. This method, however, has the disadvantages that the service life of the belt is significantly reduced under the pressure of the increased tension, and also the pulley axles may bend or the pulley bearings may wear .~, ~
,, ~ ji. ', : . .
rapidly as a result of the greater load applied to the pulleys.
These days, highly complex meehanisms employing tension belts are generally enclosed easings of the prescribed capacity for automobiles, computers and various other machines. Accordingly, when a transmission belt becomes loose, re-tensioning of the belt requires dis-assembling, replacing and re-assembling of the machine.
This requires much time and labor.
As the following description refers to the accom-panying drawings, all of the drawings will first be introduced for elarity, as follows:
Fig. 1 shows a eross section of a V belt according to one embodiment of the present invention;
Fig. 2 and Fig. 3 show respectively an outline of the testing apparatus for a V belt;
Fig. 4-A and Fig. 4-B show respectively the relation between belt tension and running hours, obtained from the result of running tests in Experiment I and Experiment II
given later; and Fig. 5 to Fig. 8 show respeetively eross seetions of eonventional V belts.
Conventional transmission belts are available in several kinds, sueh as flat belts and V-belts. Fig. 5 to Fig. 7 show eross seetions of eonventiontal V belts, in whieh a is a surfaee eanvas; b is adhesive rubber; e is a polyester fiber eord; dl is eareass fabric; e is bottom rubber; f is a bottom eanvas and d2 is a rubber layer with fibers oriented about 90 to the longitudinal axis of the belt.
If a V belt is used for a ear engine, for example, the initial tension of the belt will be reduced due to its residual strain in proportion to running distance. Causes of such elongation of the belt are roughly divided into:
(1) apparent elongation due to the belt descending further into the groove of a pulley as a result of abrasion at both sides of the belt; (2) real elongation of polyester fiber cords embedded in the V belt; and (3) apparent elon-gation due to the deformation of the cross sectional shape of the belt caused by lateral pressure applied to the sides of the belt during running. The aggregate of these three factors brings about a gradual reduction of tension, with resultant elongation of the belt which causes belt slippage. It has been the usual practice that when elongation of the belt occurred, tensioning of the belt, namely, adjusting of the belt tension, has been carried out.
In order to decrease the requirement for belt re-tensioning, or to dispense with belt re-tensioning altogether, it is necessary to prevent such elongation of the belt. In this respect, it has been suggested to use, as belt reinforcement, polyester fiber cords of such pro-perty that their elongation at 100C and that at 24C are almost equal, for the purpose of minimizing the elongation of the cords (U.S. Patent No. 3,469,001). However, such a belt with polyester fiber cords embedded therein is still stretched on pulleys at a high initial tension (the lowest tension at which no slippage takes place plus 50% or more extra tension) to increase the time required for re-tensioning of the belt. However, as stated above, since the belt is stretched on pulleys at such a high tension, a large load is applied to both the pulley axles and the , ~,. . .
;r ~' "~
bearings, with resultant bending of the axles and wearing of the bearings. Furthermore, the belt is sensitive to shock load because a high factor of safety cannot be provided for the belt as it is anyway over tensioned and therefore trouble at an initial stage will increase.
From the above, it can be seen that a belt in which polyester fiber cords of the above-mentioned type are embedded is improved with respect to the elongation of the cords, but elongation due to other factors remains unimproved and therefore the belt tension will be gradually reduced. On the other hand, if the belt is installed on pulleys at a tension lower than the lowest tension at which belt transmission is possible, belt slippage occurs immediately after the start of belt running and re-tensioning must be carried out. Also, if polyester fiber cords c of very high shrinkage tension are used for the V belt having neither woven fabric dl nor rubber layer d2 shown in Fig. 6, the cords c in the transmission belt will become partially buried in the bottom rubber e as shown in Fig. 8, during the vulcan-izing process and as a result the arrangement of cords will be disordered. In order to prevent this problem, it will bé necessary to increase the viscosity of the bottom rubber e shown in Fig. 8 or to employ a construction as shown in Fig. 5 and Fig. 6. In the typical conventional belt having polyester fiber cords, the cords are made of polyester yarn having the following characteristics.
;i r3 Relative viscosity: 0.60 - 0.70 (dissolved in orthochlorophenol) Tenacity: 7.5 - 8.5g/D
Elongation: 11 - 15%
Heat shrinkage: 5 - 10~ (held for 30 minutes at 150C) Shrinkage tension: 0.2 - 0.4g/D (at 185 - 215C) (maximum tension) In the above characteristic values, g represents gram and D represents the denier of the fiber. The relative viscosity of polyester yarn was obtained in the following way, namely 29 of polyester fiber was dissolved in 25ml orthochlorophenol; the viscosity was then measured by Ostwald's viscosimeter; the measured value was divided by the viscosity of orthochlorophenol, multiplied by 0.024 and then 0.02634 was added. The tenacity and elongation were measured according to JISL-1017-1963 (constant speed stretching type). Hat shrinkage was measured according to JISL-1017-1963.5.12 by maintaining a sample for 30 minutes at 150C. Shrinkage tension was measured according to JISL-1017-1963.5.13 at a temperature ranging from 185C to 215C and the maximum value obtained throughout the whole measurement was made the shrinkage tension.
According to the invention there is provided an auto-matic tension transmission belt having polyester fiber cords embedded therein, characterized in that said poly-ester fiber cords shrink at a temperature of 80C or higher, so that, when the belt is installed between two pulleys for the transmission of force therebetween, the frictional heat generated by any slippage of the belt causes the fiber cords to shrink at the said temperature, thereby increasing the belt tension and eliminating said slippage.
,~
The automatic tension transmission belt according to the present invention uses polyester fiber cords as the core materials. These are preferably made by twisting polyester fiber yarn having a relative viscosity of 0.90 - 1.30 in solution in orthochlorophenol and a maxi-mum shrinkage tension of 0.40 - 0.55g/D at a temperature ranging from 180C to 215C, are subjected to a hot stretching process of more than 5% elongation percentage by multi-stage stretching and are embedded in rubber constituting the belt, while maintaining the proper thermal force of polyester fiber cords during the vul-canizing process of said rubber. While such belt is running, the above-mentioned polyester fiber cords shrink by their thermal contractile force at a frictional heat of higher than 80C generated by belt slipping caused by lowering of belt tension. Thus, the belt tension recovers to the minimum tension necessary for transmission of power, thereby eliminating belt slipping and maintaining its tension at a regular level, with automatic repetition of such re-tensioning if further slipping occurs.
An embodiment of the present invention is explained below, with reference to a V belt. Fig. l shows a cross section of a V belt l according to-the present invention.
Numeral 2a denotes a surface canvas. Numeral 2b denotes a bottom canvas. Numeral 3 denotes adhesive rubber.
Numeral 4 denotes a polyester fiber cord to which a special drafting process has been imparted. Numeral 5 is a bottom rubber.
The above-mentioned polyester fiber cord 4 was made by twisting material yarn having the following characteristics:
, Relative viscosity: 0.90 - 1.30 (dissolved in orthochlorophenol) Tenacity: 8.5 - 9.5g/D
Elongation: 12 - 15~ (elongation at break) Heat shrinkage: 8 - 11% (held for 30 minutes at 150C) Shrinkage tension: 0.4 - 0.55g/D (the maximum tension at 180 - 215C) Where: g = gram D = Denier of fiber The relative viscosity, etc. were measured in the afore-mentioned way.
The above-mentioned cord 4 is subjected to an adhesion treatment and a heat drafting treatment. The adhesives used for the adhesion treatment may be, for example, iso-cyanate type adhesives, epoxy type adhesives, RFL, etc.
The hot stretching process is carried out by a multi-stage stretching at a stretching percentage of more than 5%, preferably the stretching percentage should be increased gradually with the progress of stretching process. Polyester fiber cords 4 to which the hot stretching process has been imparted are embedded in the above-mentioned bottom rubber 5 as tensile members. When vulcanizing the bottom rubber, care should be taken to ensure that the thermal contractibility of the cords 4 is not impaired, for example, rubber vulcanizable at a low temperature may be used as the material for the bottom rubber 5 to increase the viscosity of the bottom rubber 5, or to interpose between the cord 4 and the bottom rubber S
a carcass or a rubber layer with fibers arranged in the direction about 90 to the longitudinal axis of the belt (please refer to Fig. 5 and Fig. 6).
While the V belt of the above-mentioned construction , ~r4,,,~ ~ 7 --is running, belt tension is reduced by generation of apparent elongation, real elongation, abrasion and defor-mation of the cord 4, and when the belt tension decreases below the minimum tension required, belt slippage takes place and the V belt 1 itself generates heat due to fric-tion. When the temperature of the V belt 1 rises above 80C due to such frictional heat, the above-mentioned polyester fiber cords 4 embedded in the V belt 1 shrink as a result of their thermal contractile properties, and if the cords 4 shrink in excess of the belt elongation percentage at which belt slippage took place, the belt recovers the minimum tension necessary for transmission of power and consequently belt slippage is eliminated.
In response to the elimination of belt slippage, the belt temperature is reduced and, accordingly, the cord 4 ceases to shrink.
When the V belt 1 elongates due to its running and belt slippage takes place again, the belt tension is again recovered automatically to the minimum tension necessary for transmission of power and to maintain tension at a regular level. In short, whenever the above-mentioned V
belt 1 elongates, irrespective of the cause of elongation, it shrinks and recovers its tension in response to the elongation.
As mentioned above, in order to enable the V belt 1 to have this automatic tensioning action, it is essential that the polyester fiber cords 4 embedded in the V belt 1 possess very high shrinkage tension. For increasing the shrinkage tension of the cord 4, firstly the material of the polyester fiber yarn itself must have a high relative viscosity (0.90 - 1.30) and a high shrinkage tension (0.40 - 0.55g/D), secondly the hot stretching process 1 ~ A
. .
to be imparted to improve the shrinkage tension of the cord 4 must be based on a multi-stage stretching of more than 5% elongation, and thirdly the shrinkage tension improved by the hot stretching process must not be reduced during the vulcanizing process. If the relative viscosity of the yarn material is increased, its strength, heat shrinkage and shrinkage tension will increase, with resultant improvement of thermal contractile force and temperature-sensitive characateristics. Similarly, the hot stretching process involving multi-stage stretching to more than 5% brings about a higher heat shrinkage and higher shrinkage tension, with the result of higher thermal force and improved temperature-sensitive char-acteristic. Thus, thermal shrinkage occurs immediately in response to an increase of belt temperature upon belt slippage and consequently the required tension is quickly recovered. It must be noted, however, that polyester fibers having a relative viscosity of more than 1.30 are difficult to manufacture.
Tests were carried out to see if the above-mentioned V belt possesses a tension recovering function and to specify such characteristic.
I. Static test (a) Testing apparatus A testing apparatus as shown in Fig. 3 was used. V
belt 1 for testing is put on flat pulleys 8, 9 supported by pulley holders 10, 11 by such a method that their rear sides make contact with the pulleys. These are put in a thermostatic chamber 7. The pulley holder 10 is hung on a load cell 6 and a loading weight 12 is suspended from the pulley holder 11.
- _ g _ , i,~,. ..
(b) Testing method In the following procedure, the above-mentioned V belt 1 is put in a condition closely resembling the condition in which it actually runs, and its characteristics are obtained. The testing procedures 1 - 6 were carried out at room temperature (20 - 25C).
Testing procedure 1 To put the V belt 1 on the pulleys 8, 9, with its rear side in contact with the pulleys.
Testing Procedure 2 (Center distance Xl) To apply a load Wl (1/8 of the tenacity at break) to the V belt 1 and read the center distance Xl in that position. To leave the V belt 1 for 10 minutes as it is and read a load W2 after relaxation of force. The load Wl corresponds to an initial tension at the time when the belt is fitted, in other words, the procedure 2 sets the condition at the initial stage of belt fitting.
Testinq procedure 3 To pull at the stretching speed of lOmm/minute. To apply a load W3 which is one-fifth of the tenacity at break and leave for one minute and then put back to the load W2 at the speed of lOmm/minute and leave for 30 seconds. This operation is repeated three times.
The load W3 corresponds to the transmission tension acting upon the tight side at belt running and the lGad W2 corresponds to the tension on the slack side. In other words, the procedure 3 sets the condition in which each poiint of the belt passes the tight side and the slack side according to the belt running.
Testing procedure 4 (Center distance X2) To pull at the stretching speed of lOmm/minute. To apply a load W3 which is one-fifth of the tenacity at break and leave for one minute and then put back to X2 (position of 0.996 x Xl) at the speed of lOmm/minute and leave for 2 minutes.
The center distance X2 moves the pulley to make the V belt generate an apparent elongation. The movement of the pulley corresponds to the elongation percentage (allowable elongation percentage) by which slip occurs in actual belt running. In other words, the procedure 4 sets the condition in which the V belt elongated due to belt running. The allowable elongation percentage C is { (Xl - X2) /Xl } X 100.
Testing Procedure 5 (Strain A and center distance X3) To pull at the st etching speed of lOmm/minute, apply a load W3, leave for two minutes and read a center distance X3.
Strain A = {(X3 - X2)/Xl} x 100 Strain A is a strain at the room temperature and at the load W3 corresponding to the transmission tension and corresponds to the strain to which the V belt is sub-jected at belt running. The larger the value of strain, the more the belt slipping tends to take place.
Testing Procedure 6 ; To put back to the point X2 at the speed of lOmm/minute and then leave for two minutes.
Testing procedure 7 To blow hot air in a thermostatic chamber 7 in the condition where the load W2 is applied after relaxing of stress and continue to heat at 80C until contractile force is made constant in hot air.
The heating temperature 80C corresponds to the . .
temperature at which heat is generated due to belt slipping, namely, the procedure 7 sets the condition in which the belt slips due to its elongation, generates heat of 80C due to frictional heat and then shrinks.
Testing Procedure 8 To pull up the load W3 at the stretching speed of lOmm/minute and read a center distance X4 at that time.
Strain B = (X4 - X2)/Xl x 100 The strain B is a strain at the temperature of 80C
and at the load W3 corresponding to the transmission tension and corresponds to the strain to which the V belt is subjected when the belt generates heat. The less the value of this strain, the more the belt slipping becomes easy to be removed.
(c) Test results Each load of Wl - W4 and each center distance of Xl - X4, together with Strain A, Strain B obtained from the load and the center distance, and an allowable elongation percentage C are shown below, in comparison between the V belt according to the present invention and the conventional V belt.
`~
~ _ .
.
V belt according to the present Conventional invention V belt Wl 56 kg 56 kg W2 48.5 kg 44.5 kg W3 90 kg 90 kg Xl 413.3mm 415.Omm X2 411.647mm 413.34mm X3 416.069mm 418.237mm X4 413.362mm 417.013mm Strain A 1.07% 1.18%
Strain B 0.415% 0.885%
A - B 0.655% 0.295%
C 0.400% 0.400%
From the above test results, it can be seen that in order to make the V belt possess the automatic tensioning action whereby the belt shrinks upon belt slipping and recovers its tension, it is required that the belt gen-erates contractile force when the temperature lS raised to 80C and the strain B at this 80C is smaller than the strain A at the room temperature. Also, it is required that the difference between the two strains or A - B is larger than the allowable elongation percentage C at the belt slippage, in other words, the belt tension after shrinking due to generation of contractile force should be the tension at the time prior to belt slippage. ~
With regard to the above requirements, both the V belt `
according to the present invention and the conventional V belt satisfy the re~uirement of A , B. However, in respect of the relation between A - B and the allowable -elongation percentage C, while the V belt according to the present invention indicates A - B > C, the conventional V
belt indicates A - B < C. This means that while the V
belt according to the present invention possesses auto-matic tensioning action, the conventional V belt shows thermal shrinkage to some extent but such thermal shrink-age is not sufficient to correct belt slippage. This point has been confirmed by the dynamic test mentioned below.
II. Dynamic test (a) Testing apparatus The testing apparatus shown in Fig. 2 was used. The V
belt 1 was installed on the driving side, the driven side and idle pulleys 13, 14, 15 with the location as shown in Fig. 2, and the running test was carried out with the belt span initial tension set at 30 kg by a belt tension gauge.
The diameter of V-grooved pulleys 13, 14, the diameter of the V-grooved idle pulley 15, the number of revolution of the V-grooved pulley 13 on the driving side and the shaft load on the driven side were 127mm, 76.2mm, 4,700 r.p.m.
and 13 ps respectively. V belt 1 of A-shape No.40 (JIS K 6323) was used.
(b) Test results Test results as shown in Fig. 4-A were obtained. In order to maintain the span tension of 30 kg, the conven-tional V belt must be re-tensioned twice, 0.1 hr. and 0.6 hr. after the start of the running, but V belt according to the present invention does not require such re-- tensioning. In this test, while the V belt according to the present invention retained the original span tension of 30 kg even at the end of 200 hours after the start of ~3~
running, the conventional V belt lowered its tension to the level of 22 kg, in spite of the re-tensioning effected twice at the early stage after the start of running, and continued to lower its tension, with the result of the difficulty of transmitting the prescribed load. Thus, further re-tension was required for the conventional V-belt.
Experiment II
(a) Testing apparatus The same testing apparatus as used in Experiment I
(refer to Fig. 2) was used. The V belt was installed on the driving side, the driven side and idle pulleys 13, 14, 15, with the belt span initial tension set at 10 kg by a belt tension gauge, and the running test was carried out.
The diameter of the V-grooved pulleys 13, 14, the diameter of the idler V-grooved pulley 15, the number of revolution of the V-grooved pulley 13 on the driving side, and the shaft load on the driven side were 127mm, 76.2mm, 4,700 r.p.m. and 13 ps respectively. V belt 1 of A-shape No. 40 (JIS K 6323) was used.
(b) Test results Test results as shown in Fig. 4-B were obtained. As the span tension was set at 10 kg, which was less than the lowest span tension necessary for load transmission, the conventional V belt was broken down in only 0.1 hours after the start of running due to a sudden slip, whereas the belt according to the present invention regained the span tension of 30 kg soon after the start of running and thereafter maintained the span tension of 30 kg. Similarly to the case of Experiment I, since the belt according to the present invention shrinks due to heat generated by 's'~ ' slippage or has an automatic tensing action, it does not require re-tensioning at all and shows recovery of tension by its own automatic tensing action even if its tension was set below the lowest tension necessary for load transmission.
In addition, various test specimens of polyester fiber material yarn were prepared, by varying the rela-tive viscosity (0.7 and 0.9), the stretching process (one-stage stretching at 3% and 5% and two-stage elongation at 5% or more) and the shrinkage percentage of polyester fiber cords before and after the vulcanizating process (0.3 - 1.3%), and each test specimen was tested for the value of shrinkage tension, based on which the value of shrinkage tension was obtained, as shown in Table 1. Also, from the results of the above-mentioned static test and the results of the dynamic test (Experiment I), the existence of automatic tensioning action of each test specimen was obtained, as shown in Table 2.
In these tests, polyester fiber material yarn of 1100 deniers, polyester fiber cords construction of 2 x 5 twist and belt of A-shape No. 40 (I.S.O. Recommendation R608 -Belt length 40 inches) were used. The maximum shrinkage tension is the maximum value at the temperature ranging from 180C to 215C. The shrinkage tension was measured according to the JIS L-1017-1963 (method of measuring the shrinkage tension upon dry heating). The hot stretching process was done at the temperature of 230C and for the exposure time of 120 seconds.
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,., , ~, In the above Table 1 and Table 2, Samples No. 12 and No. 13 represent transmission belts having automatic tensing action. These samples required no re-tensioning even after a 200-hour run. Those samples which showed a relative viscosity of 0.7 (Sample No. 1 - No. 6) were low in the maximum shrinkage tension (0.31g/D) of material yarn and therefore the shrinkage tension of cord was small (0.30g/D), although they were elongated at two-stage 5%
stretching percentage and their shrinkage percentage at vulcanizing was made 3% (Sample No. 6). Thus, these samples had no automatic tensing action and required re-tension after only one-hour running.
On the other hand, among the samples which showed a relative viscosity of 0.9 and a maximum shrinkage tension of 0.45g/D for their polyester fiber material yarn (Samples No. 7 - No. 13), those which were stretched at 3% in the hot stretching process (Samples No. 7 and No. 8) and those which were stretched at 5% but by one-stage stretching (Samples No. 9 and No. 10) had no automatic tensing action, even though the shrinkage percentage at vulcanizing was low, and required re-tension after running for 0.5 - 85 hours. Even in the case of the hot stretching process by two-stage stretching at 5% or more, the sample which showed a high shrinkage percentage (1.3%) at vulcanizing (Sample No. 11) was reduced in the shrinkage tension of cord after vulcanizing (0.25g/D), with the result that it had no automatic tensioning action and required re-tensioning after running for 10 hours.
In the above Table 1 and Table 2, the conventional V
belt and the V belt according to the present invention mentioned in the foregoing static test and dynamic test ~ .
t;~i~
correpond to Sample No. 3 and Sample No. 13 respecti~ely.
The above embodiments of the present invention refer to the V belt but the present invention is not limited to the V belt but is applicable to any frictional transmission belt, such as a flat belt.
As mentioned above, the belt according to the present invention shrinks due to heat generation by slippage, or has the automatic tensioning action, and therefore it has a big advantage in that it does not require re-tensioning.
This produces the advantage that no excessive load need be applied to the belt because the belt can be installed at the prescribed load transmission tension from the initial stage, mechanical precision of the shaft can be kept in good condition and bearings are free from damage. In addition, the elimination of the need for re-tensioning brings high efficiency to the maintenance of machines.
. . ..
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,., , ~, In the above Table 1 and Table 2, Samples No. 12 and No. 13 represent transmission belts having automatic tensing action. These samples required no re-tensioning even after a 200-hour run. Those samples which showed a relative viscosity of 0.7 (Sample No. 1 - No. 6) were low in the maximum shrinkage tension (0.31g/D) of material yarn and therefore the shrinkage tension of cord was small (0.30g/D), although they were elongated at two-stage 5%
stretching percentage and their shrinkage percentage at vulcanizing was made 3% (Sample No. 6). Thus, these samples had no automatic tensing action and required re-tension after only one-hour running.
On the other hand, among the samples which showed a relative viscosity of 0.9 and a maximum shrinkage tension of 0.45g/D for their polyester fiber material yarn (Samples No. 7 - No. 13), those which were stretched at 3% in the hot stretching process (Samples No. 7 and No. 8) and those which were stretched at 5% but by one-stage stretching (Samples No. 9 and No. 10) had no automatic tensing action, even though the shrinkage percentage at vulcanizing was low, and required re-tension after running for 0.5 - 85 hours. Even in the case of the hot stretching process by two-stage stretching at 5% or more, the sample which showed a high shrinkage percentage (1.3%) at vulcanizing (Sample No. 11) was reduced in the shrinkage tension of cord after vulcanizing (0.25g/D), with the result that it had no automatic tensioning action and required re-tensioning after running for 10 hours.
In the above Table 1 and Table 2, the conventional V
belt and the V belt according to the present invention mentioned in the foregoing static test and dynamic test ~ .
t;~i~
correpond to Sample No. 3 and Sample No. 13 respecti~ely.
The above embodiments of the present invention refer to the V belt but the present invention is not limited to the V belt but is applicable to any frictional transmission belt, such as a flat belt.
As mentioned above, the belt according to the present invention shrinks due to heat generation by slippage, or has the automatic tensioning action, and therefore it has a big advantage in that it does not require re-tensioning.
This produces the advantage that no excessive load need be applied to the belt because the belt can be installed at the prescribed load transmission tension from the initial stage, mechanical precision of the shaft can be kept in good condition and bearings are free from damage. In addition, the elimination of the need for re-tensioning brings high efficiency to the maintenance of machines.
. . ..
Claims (5)
1. An automatic tension transmission belt having poly-ester fiber cords embedded therein, characterized in that said polyester fiber cords shrink at a temperature of 80°C
or higher, so that, when the belt is installed between two pulleys for the transmission of force therebetween, the frictional heat generated by any slippage of the belt causes the fiber cords to shrink at the said temperature, therby increasing the belt tension and eliminating said slippage.
or higher, so that, when the belt is installed between two pulleys for the transmission of force therebetween, the frictional heat generated by any slippage of the belt causes the fiber cords to shrink at the said temperature, therby increasing the belt tension and eliminating said slippage.
2. A belt according to claim 1 wherein polyester fiber yarn constituting said polyester fiber cords have a relative viscosity in solution in orthochlorophenol of 0.90 - 1.30.
3. A belt according to claim 1 wherein the maximum shrinkage tension of polyester fiber yarn constituting said polyester fiber cords at a temperature of 180° -215°C is 0.40 - 0.55g/D.
4. A belt according to claim 1, claim 2 or claim 3 wherein said polyester fiber cords have been subjected to a prior treatment of multi-stage stretching of more than 5%.
5. A belt according to claim 1, claim 2 or claim 3 formed in such a way that shrinkage of said polyester fiber cords is avoided at the time of vulcanizing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA315,747A CA1112078A (en) | 1978-11-02 | 1978-11-02 | Automatic tension transmission belt |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA315,747A CA1112078A (en) | 1978-11-02 | 1978-11-02 | Automatic tension transmission belt |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1112078A true CA1112078A (en) | 1981-11-10 |
Family
ID=4112871
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA315,747A Expired CA1112078A (en) | 1978-11-02 | 1978-11-02 | Automatic tension transmission belt |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1112078A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110491606A (en) * | 2019-08-02 | 2019-11-22 | 金杯电工电磁线有限公司 | Glass fiber winding wire apparatus for baking |
-
1978
- 1978-11-02 CA CA315,747A patent/CA1112078A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110491606A (en) * | 2019-08-02 | 2019-11-22 | 金杯电工电磁线有限公司 | Glass fiber winding wire apparatus for baking |
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