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Subchapter 13. Logging and Sawmill Safety Orders
Article 17. Lath, Shingle, and Shake Mills

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§6402. Bolters and Lath Machines, Appendix B


Engineering Data

Strength and Weights of Wire Ropes

 
Breaking Strength                                             
Rope Diameter              Plow Steel in Tons  Weight Per Foot
in Inches                  6x 19 6 x17 6 x 21  in Pounds      
1/4..............   2.39   .10                                
5/16.............   3.71   .16                                
3/8..............   5.31   .23                                
7/16.............   7.19   .31                                
1/2..............   9.35   .40                                
9/16.............   11.8   .51                                
5/8..............   14.5   .63                                
3/4..............   20.7   .90                                
7/8..............   28.0   1.2                                
1................   36.4   1.60                               
1 1/8............   45.7   2.03                               
1 1/4............    56.2  2.50                               
1 3/8............   67.5   3.03                               
1 1/2............    80.0  3.60                               
1 5/8............    93.4  4.23                               
1 3/4............   108.0  4.90                               
1 7/8............   123.0  5.63                               
2................   39.0   6.40                               
2 1/8............   156.0  7.23                               
2 1/4............   174.0  8.10                               
2 1/2............   212.0  10.00                              
2 3/4............   254.0  12.10                              
3................  300.0   15.00                              
 
 
When ropes are galvanized deduct 10 percent from the above listed strengths. When wire strand centers and independent wire rope centers are used add 7 1/2 percent to strengths.

Common Causes of Wire Rope Failure

1. Ropes of incorrect size, construction, or grade

2. Ropes allowed to drag over obstacles

3. Ropes not properly lubricated

4. Ropes operating over sheaves and drums of inadequate size

5. Ropes overwinding or crosswinding on drums

6. Ropes operating over sheaves and drums out of alignment

7. Ropes operating over sheaves and drums with improperly fitting groves or broken flanges.

8. Ropes permitted to jump sheaves

9. Ropes subjected to moisture of acid fumes and salt air

10. Ropes with improperly attached fittings

11. Ropes permitted to untwist

12. Ropes subjected to excessive heat

13. Ropes kinked

14. Ropes subjected to severe overloads due to inefficient operation

15. Ropes destroyed by internal wear caused by grit penetrating between strands and wires.

Rules for Discarding Wire Ropes

1. Safety factors must never fall below 4.5

2. Ropes of standard construction shall be discarded where there are 6 broken wires in 1 rope lay

3. When wires on crown are worn to 65 percent of their original diameter

4. When there are more than 8 broken wires reduced by wear more than 80 percent in cross-section

5. When marked corrosion appears When a new rope is installed, there is a short period (while the rope is taking its set and equalizing tension) during which breaks are relatively frequent. These breaks do not necessarily indicate that the rope is wearing out or that it is overstressed. After the period of their occurrence, the rope will run for sometime without more wires breaking. Toward the end of the life of the rope, however, it may happen that the number of breaks begins to increase rapidly. This condition is a sign that the rope is going to pieces and it should be taken off immediately. It is recommended, therefore, that not only should rope inspections be frequent, but that the number of broken wires be recorded so that the increase in breaking rate may be ascertained.

STRENGTH EFFICIENCY UNDER STATIC LOAD

 
 Sheave Diameter            Efficiency of Rope               
10 times rope diameter....  79% of strength of straight rope 
12 times rope diameter....  81% of strength of straight rope 
14 times rope diameter....   86% of strength of straight rope
16 times rope diameter....  88% of strength of straight rope 
18 times rope diameter....   90% of strength of straight rope
20 times rope diameter....  91% of strength of straight rope 
24 times rope diameter....  93% of strength of straight rope 
30 times rope diameter....  95% of strength of straight rope 
 
 
EXAMPLE: Given a 1-inch rope (breaking strength 36.4 tons) reeved through a 10- inch pulley. The strength of the rope is (36.4) (.79) = 28.75 tons. (Based on U.S. Bureau of Standards tests.)

APPLICATION OF CLIPS

 
Diameter of Rope....  Number of Clips  Space Between Clips
1 1/2 inch..........  8                10 inches          
1 3/8 inch..........  7                9 inches           
1 1/4 inch..........  6                8 inches           
1 1/8 inch..........  5                7 inches           
1 inch..............  5                6 inches           
7/8 inch............  5                5 1/2 inches       
3/4 inch............  5                4 1/2 inches       
3/8-5/8 inch........  4                3 inches           
 
 
Proper number ad spacing to develop 80 percent of rope strength.

EFFECTIVENESS OF GUYS ACCORDING TO ANGLE

Guys making angle with the horizontal greater than 60 will be considered less than 50% effective.

 
 Degree           Effectiveness
60 5 to 45 5....   50% to 75%  
45 5 to 30 5....  75% to 85%   
30 5 to 10 5....  85% to 95%   
 
 
EFFECTIVENESS OF GUYS ACCORDING TO NUMBER AND SPACING

 
 No. Guys                                                        
Equally    Guys Most Effective        Guys Will Support Strain   
Spaced     When Pull Is               Equal to Following         
3          Opposite 1 guy             100% of strength of one guy
4          Halfway between 2 guys     140% of strength of one guy
5          Opposite 1 guy or halfway                             
           between 2 guys             160% of strength of one guy
6          Opposite 1 guy or halfway                             
           between 2 guys             200% of strength of one guy
7          Opposite 1 guy or halfway                             
           between 2 guys             225% of strength of one guy
8          Halfway between 2 guys     260% of strength of one guy
9          Opposite 1 guy or halfway                             
           between 2 guys             290% of strength of one guy
10         Opposite 1 guy or halfway                             
           between 2 guys             325% of strength of one guy
 
 
LENGTH OF GUYS REQUIRED FOR VARIOUS ANGLES OF EFFICIENCY

The following table will furnish the answers to the following problems which usually arise when making up guy lines.

 (1) What length of line is needed to reach from a certain height to the ground with the required angle of efficiency? 


 (2) If the guylines are already cut and the required angle of efficiency is known, how high above the ground can the guys be rigged? 


 (3) If you know how high the guys are to be rigged above the ground, the length of guys and the angle of efficiency needed, how far away from the base of the spar or mast should stumps be selected or "deadmen" be placed to hold the guys? 


30o Angle of Efficiency 45o Angle of Efficiency 60o Angle of Efficiency
Height above ground at Which Guys Are Fastened to Tree Lenght of Guys Necessary to Make Angle of 30o With Horizontal Distance Away From Foot of Spar Tree or Mast That Guys Will Meet Level Ground at 30o Angle Lenght of Guys Necessary to Make Angle of 45o With Horizontal Distance Away From Foot of Spar Tree or Mast That Guys Will Meet Level Ground at 45o Angle Lenght of
Guys Necessary to Make Angle
of 60o With Horizontal
Distance
Away From Foot of Spar Tree or Mast That Guys
Will Meet Level Ground
at 60o Angle
30 60 51.99 42.43 30 34.64 17.34
35 70 60.66 49.50 35 40.42 20.23
40 80 69.32 56.58 40 46.19 23.12
45 90 77.99 63.65 45 51.96 26.01
50 100 86.65 70.72 50 57.74 28.90
55 110 95.32 77.79 55 63.51 31.79
60 120 103.98 84.87 60 69.28 34.68
65 130 112.65 91.94 65 75.06 37.57
70 140 121.31 99.01 70 80.83 40.46
75 150 129.98 106.08 75 86.60 43.35
80 160 138.64 113.15 80 92.38 46.24
85 170 147.31 120.23 85 98.15 49.13
90 180 155.97 127.30 90 103.93 52.02
95 190 164.64 134.37 95 109.70 54.91
100 200 173.30 141.44 100 115.47 57.80
110 220 190.63 155.58 110 127.02 63.58
120 240 207.96 169.63 120 138.57 69.36
130 260 225.29 183.87 130 150.11 75.14
140 280 242.29 198.02 140 161.66 80.92
150 300 259.95 212.16 150 173.21 86.70

 
 No. of  Guys Most Effective        Guys Will Support Lead   
Guys     When Pull Is               Equal to:                
   8     Halfway between 2 guys     260% of strength of 1 guy
   9     Either halfway between 2,  290% of strength of 1 guy
         or opposite 1 guy                                   
 
 
 EXAMPLE: In lifting a 10-ton log between spreader bar rigger spar poles the horizontal force at the top of the pole is found to be 25 tons. Using a factor of safety of 5 the design strength of 1 1/2-inch guys is 


 
80.0  = 16 tons. If the spar pole guys are rigged at 80 angle with the ground,
----                                                                          
 5       they are 85% effective (see table). How many guys should be used?    
 
 
 
25            = 1.84 or 184%
------------                
(16) (.85)                  
 
 
 The number of guys needed to support 184% of strength of 1 guy in between 5 and 6 (see table). Therefore, 6 guys should be used with 1 1/2-inch cable. Other cable sizes will give a variety of numbers of guys for more practicable application. 


INDIRECT METHOD OF DETERMINING THE LOAD ON A WIRE ROPE.

 Since 1 horsepower is the rate at which 550 foot-pounds of work are done per second, the horsepower exerted by an engine on a rope may be expressed: 


 
HP =   feet x pounds
      --------------
seconds x 550       
 
 
 
By rearrangement:                                    
 Pull on rope in pounds =  horsepower x seconds x 550
                           --------------------------
                           feet                      
 
 
 Thus if you know the horsepower of a given engine and measure the number of seconds it takes a point on the rope to go a given distance the pull on the rope may be found. 


 EXAMPLE: A 100-HP gasoline donkey engine requires 10 seconds to reel in 30 feet of cable when working at nearly wide-open throttle. What is the pull on the cable? 


 Since 100 HP is the ideal SAE rating of a stripped engine it is not a true indication of the power delivered at the cable. A good assumption is 1/3 of rated horsepower. 


 
Pull on rope in pounds  = 33 x 10 x 550                 
                        ________________  = 6,050 pounds
                           30                           
 
 
 Providing a safety factor of 5 the required rope strength should be 30,250 pounds or 15.2 tons. From the table on page 112, in Appendix B, a 5/8-inch cable is nearest to this strength. 



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