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Performance of coated floats in different soils
Journal of Terramechanics, Vol. 29, No. 2, pp. 173-185, 1992. Printed in Great Britain.
0022-4898/9255.00+0.00 Pergamon Press Ltd © 1992 ISTVS
P E R F O R M A N C E OF C O A T E D FLOATS IN DIFFERENT SOILS E.
CANILLAS,*
V. M. SALOKHE* and D. GEE-CLOuGH*
Summary--Experiments were conducted in a laboratory soil bin to evaluate the performance of coated floats in different soils. Two coating materials were studied, namely enamel and Teflon, and three soil types, namely clay, loam and sandy soil were used for testing. The forces required to overcome the drag of the floats and pull them over the soil surface were measured. The normal loads were varied to 25, 44 and 64 N. The effect of moisture content (db) was evaluated by varying the soil moisture from 21.2 to 62.4% for clay soil, 16.6 to 36.1% for loam soil and 0.7 to 13.8% for sandy soil. All tests were conducted at a constant speed of 0.20 m/s. The performance of the enamel coated float was superior to Teflon and uncoated floats in all soil conditions. In clay and loam soils, the drag force increased initially until the soil moisture content reached the plastic limit. The drag forces showed a decreasing trend once soil moisture exceeded the plastic limit. In sandy soil, the drag force increased with increase in moisture content. The overall reductions for the enamel coated float compared to uncoated float were from 4 to 64% in clay soil, 16 to 46% in loam soil and 26 to 45% in sandy soil. Besides this superior performance, the enamel coated float compared to the other floats showed excellent resistance to wear due to abrasion and superior scouring.
INTRODUCTION
KEPNER et al. [1] stated that in the agricultural production system, the tillage operation accounts for more traction energy than any other field operation. The present implement designs are almost standardized. These designs work well in the field. Therefore, improvements can only be made by reducing their energy requirements. Reduction in the draft requirements would greatly reduce the power required. Most primary cultivation implements need high draft forces and any reduction would bring large benefits. O'Callaghan and McCoy [2] found that the soil friction and adhesion forces of a plough contributed 28% of the total draft. In view of the fact that soil-metal interaction contributes a great portion of the draft required for tillage implements, recent studies at the Asian Institute of Technology (AIT) gave due consideration to this subject. Salokhe and Gee-Clough [3,4] and Salokhe et al. [5] studied the possibilities of reducing the draft of tillage implements in wet clay soil by the application of coating materials on the lug surfaces, floats and mouldboard ploughs. Their studies showed that enamel coating was the most promising coating material for reducing clay soil adhesion and friction considerably. Considering that tillage operations are performed in both dryland and wetland conditions under varying soil types and working conditions, it is therefore important to investigate and quantify the benefits which can be obtained from the use of surface coating in these conditions. *Division of Agricultural and Food Engineering, Asian Institute of Technology, Bangkok, Thailand. 173
174
E. CANILLASet al.
LITERATURE REVIEW ......... Kumer and Nichols [6] found t h a t the friction between the soil and metal surfaces had a great influence upon the draft of tillage tools because the intensity of this frictional force governs largely the wearing and scouring properties of the implement. Soehne [7] found that coefficient of friction increased with an increase in the length of the sliding path in different types of soils. This was the greatest at low moisture content. Gee-Clough [8] summarized the results of several researches on wetland traction problems. Regarding floats and skids, he revealed the importance of shape and the presence of a thin film of water in reducing the drag requirement. Many researchers [9-12] reported that friction is greatly modified by adhesion. Adhesion results primarily from moisture films that increase the perpendicular attractive forces between soil and the sliding surface of the tool. Adhesion may be reduced by using a material t h a t does not readily wet with water. The type and smoothness of the material on which the soil slides affect the adhesive properties [12-16]. The sources of adhesion are many and may include molecular, electrical, Coulomb and capillary forces. Of these, the most important source for off-road vehicles is capillary forces [17]. In the past, polytetrafluoroethylene (PTFE) and polyethylene, which have non-wettable characteristics, were used as coatings on mouldboard ploughs and other tools [12, 18]. Cooper and McCreery [9] found that when the lack of scouring is a problem, PTFE can improve scouring and that draft may be reduced by as much as 25%. Once applied to a surface, the material remains effective until it is worn away by the abrasive action of the soil. Gill and Vandenberg [19] pointed out that PTFE coating may be one of the factors which could eliminate the formation of soil bodies in front of tools. Wismer et al. [20] reported that covering a plough bottom with Teflon reduced the draft by 23% in soil where steel would not scour. However, Teflon showed very poor resistance to wear and abrasion. Many other attempts made to reduce friction and adhesion on a tool surface are listed by Koolen and Kuiper [12]. Salokhe and Gee-Clough [3, 4] studied the effect on soil adhesion of coating various materials on lug surfaces, floats and mouldboard ploughs. Results showed that the coating of such surfaces significantly affected the soil adhesion. They further reported that among the materials they used in their study, enamel coating was found to be the most promising. Salokhe et al. [5] studied the effect of coating materials on the forces required to pull floats in clay soil. They observed that by applying enamel coating, the drag force could be reduced by up to 50%. Suharno [21] studied the effect of enamel coating on the specific draft of a mouldboard plough in Bangkok clay soil. He reported that the overall reduction in the draft was in the range 8-23%. Salokhe et al. [22] studied the effect of surface coating on cage wheel lug forces in a laboratory soil bin and reported that at constant sinkage, slip and soil moisture content, the lug forces generated by a coated lug did not differ significantly from those generated by an uncoated lug. METHODOLOGY The experiments were conducted in a laboratory soil bin of 300 x 80 x 60 cm size (Fig. 1) [23]. Floats of 30 cm length and 15 cm width which were fabricated from mild
C O A T E D FLOATS IN DIFFERENT SOILS
5 •
50
175
300
~1
Plan Soil
- -
-
-
Soil bin Drum Electric motor Chain Sprocket Pulley
Load cells Floot
Side view
-- I~/~/lllll/ll///I,//I///I
/ i/lll.~////i//i///////i/i All dimensions in cm
Flo. 1. Schematic of experimental set up.
steel of 0.32 cm thickness were used for testing (Fig. 2). Two floats were coated with enamel and Teflon while the third was uncoated. The enamel coating was done in the same way as coating of home utensils. A solution was made from the enamel powder and was applied to the float and then it was baked in a furnace at about 700-800 °C. Teflon in liquid form was sprayed on the cleaned float and then it was baked. The uncoated float was cleaned and degreased. Three types of soil were used for testing, namely clay, loam and sandy. The average values of the moisture and cone index and other properties of these soils are listed in Tables 1-4.
FiG. 2. The floats used in the experiments: (a) enamel coated, (b) Teflon coated, (c) uncoated.
176
E. CANILLAS et al. TABLE1. PARTICLESIZEDISTRIBUTIONAND CONSISTENCYLIMITSOF THE THREESOILS Soil type
Soil characteristics Particle size distribution Clay (%) Silt (%) Sand (%) Consistency limits Liquid limit Plastic limit Plasticity index (%) Sticky limit (%)
TABLE2.
Moisture content (db) (%)
Clay
Loam
Sandy
56.1 35.4 8.5
16.3 36.1 47.6
00 2.8 97.2
47.2 23.5 23.7 34.1
32.5 20.3 10.2 23.8
m
m
m
COHESION AND ADHESION PROPERTIES OF CLAY SOIL
Cohesion properties
Adhesion properties
Cohesion (kPa)
Angle of internal friction (deg)
Material
Adhesion (kPa)
Soil material friction angle (deg)
21.2
23.4
24.1
27.8
19.4
19.6
33.6
15.2
16.3
40.4
8.3
11.2
62.4
--
--
Enamel Teflon Uncoated Enamel Teflon Uncoated Enamel Teflon Uncoated Enamel Teflon Uncoated Enamel Teflon Uncoated
1.4 2.1 2.6 2.0 2.2 4.4 4.3 5.1 5.8 4.8 5.6 6.3 ----
16.2 17.1 18.2 14.4 14.3 16.1 13.3 14.1 14.9 11.2 12.1 12.6 ----
Soil specific weight (kN/m 3)
Cone index (kPa)
18.2
1046
18.4
924
17.9
678
18.1
493
17.4
21
T h e floats were placed h o r i z o n t a l l y o n the soil surface a n d desired n o r m a l loads were m o u n t e d at a p o i n t b e h i n d the c e n t e r of gravity of the floats [24]. T h e forces r e q u i r e d to pull the floats a l o n g the soil b i n were m e a s u r e d . T h r e e types of floats were p u l l e d parallel in each test r u n by m e a n s of a trolley which was p u l l e d by a v a r i a b l e speed m o t o r . A c o n s t a n t p u l l i n g speed of 0.20 m/s was used to avoid the effect of i n e r t i a a n d h y d r o d y n a m i c forces [24]. T h r e e s t a n d a r d load cells h a v i n g a capacity of 1000 N were used to sense the force r e q u i r e m e n t for each float. A pulley was p r o v i d e d a n d p r o p e r l y a d j u s t e d to m a t c h with the height of the c e n t e r of the load cell. P r i o r to using, the load cells were calibrated. A strain amplifier was used to amplify the o u t p u t signals from the bridge circuit of the load cells. D a t a were r e c o r d e d o n a data logger a n d t r a n s f e r r e d to a m i c r o c o m p u t e r for f u r t h e r analysis.
177
COATED FLOATS IN DIFFERENT SOILS T A B L E 3. COHESION AND ADHESION PROPERTIES OF LOAM SOIL
Moisture content (db) (%)
Adhesion properties
Cohesion properties
Soil specific weight (kN/m 3)
Cone index (kPa)
Cohesion (kPa)
Angle of internal friction (deg)
Material
Adhesion (kPa)
Soil material friction angle (deg)
16.6
15.1
28.6
Enamel Teflon Uncoated
1.2 1.8 2.3
16.8 17.4 18.2
16.4
1134
21.3
12.6
23.9
Enamel Teflon Uncoated
1.5 2.2 3.8
15.1 15.6 16.2
16.8
897
24.0
8.2
18.4
Enamel Teflon Uncoated
3.8 4.5 4.8
12.3 12.9 13.8
16.0
758
27.6
7.4
14.2
Enamel Teflon Uncoated
4.6 5.1 6.1
9.6 10.4 11.0
16.1
562
Enamel Teflon Uncoated
----
----
15.6
20
36.1
TABLE 4. COHESION AND ADHESION PROPERTIES OF SANDY SOIL
Moisture content (db) (%)
Cohesion properties Cohesion (kPa)
Adhesion properties
Angle of internal friction (deg)
Material
Adhesion (kPa)
Soil material friction angle (deg)
Soil specific weight (kN/m 3)
Cone index (kPa)
0.7
0
37.4
Enamel Teflon Uncoated
0 0 0
18.7 20.9 22.6
14.4
621
5.1
0.121
35.3
Enamel Teflon Uncoated
0.013 0.023 0.029
18.2 20.4 22.3
14.8
671
9.4
0.133
34.6
Enamel Teflon Uncoated
0.018 0.032 0.037
18.1 20.2 22.1
14.7
642
12.2
0.135
33.2
Enamel Teflon Uncoated
0.021 0.034 0.038
17.9 20.0 21.8
14.6
651
13.8
0.143
33.4
Enamel Teflon Uncoated
0.024 0.033 0.038
17.6 19.7 21.7
14.7
592
RESULTS AND DISCUSSION
Performance of floats in clay soil F i g u r e 3 s h o w s t h e a v e r a g e d r a g f o r d i f f e r e n t f l o a t s a t v a r i o u s n o r r ~ a l l~-,~ ., , 21.2% moisture content. All floats had the same contact area and were subjected to
178
E. CANILLAS
et al.
55
Surface coating I
30
I~
I I
Enamel
I ~ Teflon
25
Uncoated
z o~ 20
~ 121
15
10
44 Normal load (N)
25
F I G . 3.
64
Average drag force of the floats in clay soil at 21.1% moisture content and different normal loads.
the same amount of sinkage. However, the sinkage was insignificant. It is evident from the figure that the enamel coated float produced the least drag force at any normal load. At 25 N normal load the enamel coated float produced 64% less drag force than the uncoated float. At 44 and 64 N normal loads it produced 59% less drag than the uncoated float. The better performance next to enamel was shown by the Teflon coated float. As the normal load increased the force required to pull all the floats also increased. The ratio, D/W, was calculated for all floats at different normal loads. It was found that for a particular float the ratio was almost the same as normal load increased. However, the uncoated float had higher ratio (0.5) while the enamel coated float had the lowest ratio (0.2) for a given normal load. The ratio for the Teflon coated float was 0.4. Figure 3 shows that the drag for the enamel coated float was significantly less than for the Teflon and uncoated floats. Figure 4 and 5 show the effect of soil moisture content on the average drag forces for each float at constant normal load. At 25 N normal load and 21.2% moisture content (Fig. 4), the average force required to pull the uncoated float was 2.75 and 1.42 times greater than the 6O
ISurfacecoatingI i Enamel
y 50
~
50
a
2O
/
A
~
I'-~- Teflon
I0
0
20
I
I
I
I
I
I
I
I
25
30
35
40
45
50
55
60
Moisture content (%)
FIG. 4. Average drag force for the floats at 25 N normal load in clay soil at different moisture contents.
COATED FLOATS IN DIFFERENT SOILS
179
140 [Surface coating
[--~[ --~-
120 I00 z
Enamel
Teflon
80
o
60
El
40 20 0 20
I
I
25
30
I
I
I
I
55 40 45 50 Moisture content {%)
I
I
55
60
FIG. 5. Average drag force for the floats at 64 N normal load in clay soil at different moisture contents.
force required for the enamel and Teflon coated floats, respectively. On the other hand, the drag for the Teflon coated float was 1.94 times greater than for the enamel coated float. Increasing the soil moisture from this level to 27.8% resulted in an increase of drag for all the floats. Such increase was very small for the Teflon coated float which had a relative increase of 7% compared to 33 and 52% for the uncoated and enamel coated floats, respectively. Considerable increase in draft force for all the floats was noticed when the soil moisture content increased to 33.6%. Compared with the dry soil condition, these forces were 3.73, 3.17 and 4.75 times greater for the uncoated, Teflon and enamel coated floats, respectively. Such increases might be intensified by the soil as it reached its plastic limit when maximum shearing stresses were expected to occur. At 40.4% moisture content, all floats produced their highest drag force. The drag values were 4.00, 4.53 and 7.33 times greater than in dry soil condition for the same floats, respectively. These increases in drag forces were due to a high clay soil adhesion at the float-soil interface (Table 2). Increasing the moisture content further to 62.4% resulted in a decrease in the drag force for all the floats. In general, the drag force for the floats in clay soil increased as the moisture content increased up to about 40% and further increase in moisture content caused a decrease in the drag force. At all moisture contents, the force required to pull the enamel coated float was the least compared to other floats. Increasing the normal load from 25 to 44 N, a similar trend of the drag force was observed. Figure 5 shows the drag force for the floats at 64 N normal load and at different moisture content. The trend of drag force for all the floats was similar to that observed for previous normal loads. As the moisture content increased the drag force increased but after attaining a peak value it dropped with an increase in moisture content. The variation in the drag force with moisture content can be well explained by the fact that in a dry soil condition, soil-metal friction is a significant component of drag force for tillage implements. As this component increases, the drag force likewise increases as soil changes properties with moisture content. In wet soil, soil-metal adhesion becomes a very significant factor. When the vector sum of the cohesive
180
E. C A N I L L A S et al.
forces is greater than the adhesive forces, soil-metal failure occurs. However, when the resultant of the adhesive forces is greater than the cohesive forces, soil-to-soil failure takes place. In the case of enamel and Teflon coated floats, less adhesive forces prevail compared to the uncoated float because of the smooth contact surface they provided. However, this argument may not hold good as the soil reaches its plastic and liquid limits. Scouring can be defined as the ability of material to allow the soil to flow over it without sticking on it. Scouring also reduces the drag of the floats. The statistical analysis by the 'F' test showed a significant difference in the drag force for the floats, The analysis of variance also showed significant effects of soil moisture content, normal loads and coating materials on the forces required to pull floats.
Performance of floats in loam soil Figure 6 shows the drag force for different floats at 16.6% moisture content in loam soil at different normal loads. The force required to pull enamel coated floats was much lower than for the Teflon and uncoated floats. At 25, 44 and 64 N normal loads the drag force for the enamel coated float was 46, 46 and 44% less than the uncoated float, respectively. At all normal loads the drag force for the enamel coated float was significantly lower than for the other two floats. Figure 7 shows the effect of loam soil moisture content on the drag force of different floats at 25 N normal load. The drag increased for all floats until the soil reached its plastic limit and then it decreased when soil moisture content increased further. The enamel coated float produced the least drag force at any moisture content. The drag force at 16.6% soil moisture content for the uncoated float was 1.9 times while for the Teflon coated float was 1.7 times greater than that of the drag of the enamel coated float. Increasing the soil moisture to 21.3% resulted in an increase in the drag forces for all floats. This increase might be caused by the increase in the adhesion between the soil and the working surfaces of the floats. At 24% soil moisture, a further increase in the drag forces was recorded. The uncoated float drag was 1.63 and 1.38 times greater than the drag force for the enamel and Teflon coated floats, respectively. Further increase in the soil moisture to 27.6% resulted in an increase in the drag
35 3025-
I Surface coating I~
Enamel
IMR Teflon
Uncoated
20-
c~
I05 i
25
I
44 Normal load (N)
I
64
FIG. 6. Average drag force of the floats in loam soil at 16.6% moisture content and different normal loads.
C O A T E D F L O A T S IN D I F F E R E N T SOILS
181
Surface coating I
--11{- Enamel
I I
Tel,on
I
4O Z
O
3O 2O 10 0 16
I
I
I
i
L
L
I
I
I
I
18
20
22
24
26
28
50
32
34
56
38
Moisture content (%)
FIG. 7. Average drag force for the floats at 25 N normal load in loam soil at different moisture contents.
forces. It was observed that the greatest drag forces for each float were produced at this soil moisture. Changing the normal load to 44 N resulted in the same trend of drag forces (Fig. 8). In the case of the uncoated float, the highest drag force was attained when the soil moisture was at 24%. It was noted that when working at 16.6% soil moisture, greater drag reduction was observed from the use of enamel instead of Teflon coating. The drag force for the uncoated float was almost equal to that of the Teflon coated float while it was 1.9 times greater than for the enamel coated float. As the soil moisture was increased to 21.3%, the drag forces for each float also increased. Increasing the soil moisture to 24% resulted in a considerable increase in the drag force for each float. It was observed that the drag force for the uncoated float was 1.7 and 1.8 times greater than the Teflon and enamel coated floats, respectively. At 27.6% soil moisture content, the drag force for the uncoated float decreased. Further increases were noticed in the case of the coated floats. It was noted that the highest drag forces were reached for both coated floats. This might be caused by a greater IOO
/ 8o -
z
Surface coating
~
I -x~ Enamel
i
/
Teflon
6o-
8
2O
0
16
I
I
I
18
20
22
I
L
I
I
24 26 28 50 Moisture content(%}
I
I
I
32
34
36
38
FIG. 8. Average drag force for the floats at 64 N normal load in loam soil at different moisture contents.
182
E. CANILLAS et al.
adhesion between the working surfaces of the floats and the soil coupled with the decrease in the cohesion between the soil particles which might have resulted in an increase of soil shearing. Increasing the soil moisture content to 36.1% resulted in a decrease in the drag force of all floats due to soil behaving like a liquid and offering less resistance to motion. At 64 N normal load, similar drag forces were noticed. The enamel coated float produced the least drag compared to the other two floats. The results of the analysis of variance revealed that the coating material, normal load and soil moisture content influenced the drag forces of floats considerably.
Performance of floats in sandy soil Figure 9 shows drag of different floats in dry soil (0.7% moisture content) at different normal loads. Even in very dry sandy soil the drag for the enamel coated float was much less than for the other floats. Compared to that of the uncoated float, the drag force for the enamel coated float at 25, 44 and 64 N normal loads was 45, 46 and 44% less, respectively. This was because the enamel coating could also reduce the friction at the float-soil interface significantly compared to the Teflon and uncoated floats. As the normal load increased the force required to pull all the floats also increased. The drag forces for each float at 25 N normal load and at varying soil moisture contents in sandy soil are shown in Fig. 10. It was observed that as the moisture content was increased, the drag force for each float also increased. The increase in drag forces with moisture content showed a different trend than that observed in clay and loam soil. At the lowest moisture content (0.7%), the reduction in the drag was about 45 and 16% for the enamel and Teflon coated floats, respectively, compared to the uncoated float. In this condition, the sand was very dry, and considering that most sandy soils are usually predominantly frictional, these results showed that enamel coating was still a promising material for reducing the soil-metal friction even in a sandy soil. The drag forces gradually increased as the soil moisture was increased up to 13.8%, which was considered as the saturated condition for this particular type of soil. It can be clearly noticed that, in these conditions, compared to the uncoated float the relative drag reduction ranged from 28 to 45% by the use of enamel coated floats. At 35
Surface cooting 30
Enamel I~
25
Teflon
17ff3 Uncoated
20
o= o
15
g c~
IO
I
25
44 Normal l o a d ( N )
64
FIG. 9. Average drag force of the floats in sandy soil at 0.70% moisture content and different normal loads.
COATED FLOATS IN DIFFERENT SOILS
183
20
15
E3 Surface coating l 5
-]I[-- Enamel -.~ Teflon
I
-[3- Uncoated 0
I I
0
i 2
i :3
I 4
I 5
I 6
~ 7
I 8
i 9
I0
I II
k 12
L I.%
14
Moisture content (%)
F~6.10. Average drag force for the floats at 25 N normal load in sandy soil at different moisture contents.
44 N normal load and in a dry condition, compared to the uncoated float, reductions of 46 and 16% in drag force for the enamel and Teflon coated floats, respectively were recorded. At 64 N normal load the reduction in the drag force was in the range 27-44% for the enamel coated float. When tested statistically, it was found that in sandy soil, normal load, soil moisture content and the coating materials had a significant effect on the drag of the floats at 99% level of significance. Figure 11 reveals the average percentage drag reduction by enamel coating on the float compared to the uncoated float in different soils and moisture contents at 25 N normal load. In all cases it was observed that an increase in moisture content caused a decrease in the benefits derived by enamel coating on the floats. In sandy soil, the overall reduction in the drag was from 45 to 28% when the moisture content increased from 0.7 to 13.8%. In loam soil the percentage reduction in the drag due to enamel poating was from 46 to 22% when the moisture content increased from 16.6 to 36.1%. In clay soil the percentage drag reduction by enamel coating compared to the uncoated changed from 64% at 21.2% moisture content to 20% at 62.4% moisture content. 70 Soil type HD- Sandy soit -<3- Loam soil
60
= .o
50 40
E3
30
o~ 20 I0 0
0
I
L
I0
20
I
I
50 40 Moisture content (%)
~
I
50
60
70
F~G. 11. Average percentage drag reduction for enamel coated float compared to uncoated float in different soils.
184
E, CANILLAS et al. CONCLUSIONS
T h e p e r f o r m a n c e o f the e n a m e l c o a t e d float was f o u n d to be s u p e r i o r to that of T e f l o n a n d u n c o a t e d floats in all soils a n d w o r k i n g c o n d i t i o n s t e s t e d in this study. F o r all floats in clay a n d l o a m soil, d r a g force i n c r e a s e d with i n c r e a s e in m o i s t u r e c o n t e n t up to the plastic limit a n d a f u r t h e r i n c r e a s e in m o i s t u r e c o n t e n t c a u s e d d e c r e a s e in the d r a g force. In s a n d y soil, h o w e v e r , t h e d r a g force i n c r e a s e d with t h e soil m o i s t u r e c o n t e n t . T h e effect o f t h e m o i s t u r e c o n t e n t , c o a t i n g a n d n o r m a l l o a d s o n the d r a g forces was f o u n d to b e statistically significant at a 99% level o f significance. D e p e n d i n g o n the n o r m a l l o a d a n d soil m o i s t u r e c o n t e n t , an e n a m e l c o a t i n g o n the float r e d u c e d the d r a g force by 4 to 64% in a clay soil, 16 to 46% in l o a m soil a n d by 26 to 45% in s a n d y soil. T h e significant d i f f e r e n c e in d r a g force for d i f f e r e n t floats c o u l d be a t t r i b u t e d to t h e d i f f e r e n c e s in the a d h e s i o n c h a r a c t e r i s t i c s of the c o a t i n g m a t e r i a l s a n d the s o i l - m a t e r i a l friction b e t w e e n the soil a n d the floats. T h e e n a m e l c o a t e d floats s h o w e d e x c e l l e n t w e a r r e s i s t a n c e while the o t h e r floats s h o w e d signs of w e a r in d r y soil c o n d i t i o n s . In a n o t h e r e x p e r i m e n t by S a l o k h e et al. [25] e n a m e l c o a t i n g has s h o w n e x c e l l e n t w e a r r e s i s t a n c e . T h e results of this s t u d y clearly r e v e a l e d that e n a m e l c o a t i n g p e r f o r m s well n o t o n l y in clay soil b u t e q u a l l y well in l o a m a n d s a n d y soil. T h e s e results a r e v e r y p r o m i s i n g a n d s h o w t h a t e n a m e l c o a t e d i m p l e m e n t s o r tools can b e u s e d to a d v a n t a g e in a wide r a n g e o f soil types.
REFERENCES [1] R. A. KEPNER, R. BAINER and E. L. BARGER, Principles of Farm Machinery, 3rd Edition. AVI Publishing Company, Westport, Connecticut (1982). [2] J. R. O'CALLAOHANand J. G. McCoy, The handling of soils by mouldboard ploughs. J. agric. Engng Res. 10(1) (1965). [3] V. M. SALOKHEand D. GEE-CLOuGH, Studies on effect of lug surface coating on soil adhesion of cage wheel lugs. Proc. 9th Int. Conf. 1STVS, Barcelona, pp. 389-369 (1987). [4] V. M. SALOKHEand D. GEE-CLouGH, Coating of cage wheel lugs to reduce soil adhesion. J. agric. Engng Res. 41(3), 201-210 (1988) [5] V. M. SALOKHE, D. GEE-CLOuG, and A. I. MuFn, Performance evaluation of an enamel coated mouldboard plough. Proc. Int. Congress agric. Engng, Dublin, pp. 1633-1638 (1989). [6] F. A. KUMER and M. L. NICHOLS, The dynamic properties of soil: a study of the nature of physical forces governing the adhesion between soil and metal surface. Agric. Engng 19, 73-78 (1938)• [7] W. SOEHNE, Suiting the plough body shape to higher speeds. GrundL landtech. 12, 51-62 (National Institute of Agricultrural Engineering Translation no. 101) (1960). [8] D. GEE-CLouGH, Special problem of wetland traction and flotation. J. agric. Engng Res. 32(3), 227-229 (1985). [9] A. W. COOPER and W. F. MCCREERY, Plastic surfaces for tillage tools. ASAE Paper No.61-649 (1961). [10] P. L. DANO, The influence of soil conditions on the effectiveness of electro-osmosis and Teflon in reducing friction. Auburn University M.S. Thesis (Unpublished) (1961). [11] W. R. Fox and L. W. BOCKHOP, Characteristics of a Teflon-covered simple tillage tool. Trans. ASAE 8(2), 227-229 (1965). [12] A. J. KOOLENand H. KUIPER, Agricultural Soil Mechanics. Springer, Berlin (1983). [13] F. R. BOWDENand D. TABOR, Friction and Lubrication. John Wiley, New York (1960). [14] G. SPooR, Design of soil engaging implements. Farm Machinery Design Eng (September 1969). [15] M. L. NICHOLS, The dynamic properties of soil (II). Soil metal friction. Agric. Engng 12, 321-324 (1931). [16] J. G. POTYONDY, Skin friction various soils and construction material. Geotechnique 11(4), 339-353 (1961). [17] A. D. ZIMON,Adhesion of Dust and Powder. Plenum Press, New York (1969). {18] R. D. PILLSBURY,Application of fluorocarbon resins in farm equipment. Agric. Engng 41, 802-803, 725, 826 (1961). [19] W. R. GILL and G. E. VANDERBERG, Soil Dynamics in Tillage and Traction. Agriculture Handbook no. 316, USDA, Washington (1968).
COATED FLOATS IN DIFFERENT SOILS
185
[20] R. D. WISMER, E. L. WEGSCHEID,H. L. LuTrf and B. E. RANING, Energy application in tillage and earth moving. Soc. Auto. Engrs 77, 2486-2496 (1968). [21] SUHARNO, Performance evaluation of an enamel coated moudboard plough. Asian Inst. Techn. M. Eng. Thesis no. AE-89-14 (unpublished) (1989). [22] V. M. SALOKHE, D. GEE-CLOUGH and S. MANSOOR, Studies on effect of surface coating on forces produced by cage wheel lugs in wet clay soil. J. Terramechanics 27(2), 145-157 (1990a). [23] E. CANILLAS,Performance of coated floats in different soils. Asian Inst. Techn. M. Eng. Thesis no. AE-90-3 (unpublished) (1990). [24] N. G. SHAH, Study of float devices for wet land machinery. Asian Inst. Techn. M. Eng. Thesis no. AE-80-20 (unpublished) (1980). [25] V. M. SALOKHE, D. GEE-CLOUGH and P. TAMTOMO, Wear testing of enamel coating rings. Soil Tillage Res. 21(1/2), 121-131 (1990b).
0022-4898/9255.00+0.00 Pergamon Press Ltd © 1992 ISTVS
P E R F O R M A N C E OF C O A T E D FLOATS IN DIFFERENT SOILS E.
CANILLAS,*
V. M. SALOKHE* and D. GEE-CLOuGH*
Summary--Experiments were conducted in a laboratory soil bin to evaluate the performance of coated floats in different soils. Two coating materials were studied, namely enamel and Teflon, and three soil types, namely clay, loam and sandy soil were used for testing. The forces required to overcome the drag of the floats and pull them over the soil surface were measured. The normal loads were varied to 25, 44 and 64 N. The effect of moisture content (db) was evaluated by varying the soil moisture from 21.2 to 62.4% for clay soil, 16.6 to 36.1% for loam soil and 0.7 to 13.8% for sandy soil. All tests were conducted at a constant speed of 0.20 m/s. The performance of the enamel coated float was superior to Teflon and uncoated floats in all soil conditions. In clay and loam soils, the drag force increased initially until the soil moisture content reached the plastic limit. The drag forces showed a decreasing trend once soil moisture exceeded the plastic limit. In sandy soil, the drag force increased with increase in moisture content. The overall reductions for the enamel coated float compared to uncoated float were from 4 to 64% in clay soil, 16 to 46% in loam soil and 26 to 45% in sandy soil. Besides this superior performance, the enamel coated float compared to the other floats showed excellent resistance to wear due to abrasion and superior scouring.
INTRODUCTION
KEPNER et al. [1] stated that in the agricultural production system, the tillage operation accounts for more traction energy than any other field operation. The present implement designs are almost standardized. These designs work well in the field. Therefore, improvements can only be made by reducing their energy requirements. Reduction in the draft requirements would greatly reduce the power required. Most primary cultivation implements need high draft forces and any reduction would bring large benefits. O'Callaghan and McCoy [2] found that the soil friction and adhesion forces of a plough contributed 28% of the total draft. In view of the fact that soil-metal interaction contributes a great portion of the draft required for tillage implements, recent studies at the Asian Institute of Technology (AIT) gave due consideration to this subject. Salokhe and Gee-Clough [3,4] and Salokhe et al. [5] studied the possibilities of reducing the draft of tillage implements in wet clay soil by the application of coating materials on the lug surfaces, floats and mouldboard ploughs. Their studies showed that enamel coating was the most promising coating material for reducing clay soil adhesion and friction considerably. Considering that tillage operations are performed in both dryland and wetland conditions under varying soil types and working conditions, it is therefore important to investigate and quantify the benefits which can be obtained from the use of surface coating in these conditions. *Division of Agricultural and Food Engineering, Asian Institute of Technology, Bangkok, Thailand. 173
174
E. CANILLASet al.
LITERATURE REVIEW ......... Kumer and Nichols [6] found t h a t the friction between the soil and metal surfaces had a great influence upon the draft of tillage tools because the intensity of this frictional force governs largely the wearing and scouring properties of the implement. Soehne [7] found that coefficient of friction increased with an increase in the length of the sliding path in different types of soils. This was the greatest at low moisture content. Gee-Clough [8] summarized the results of several researches on wetland traction problems. Regarding floats and skids, he revealed the importance of shape and the presence of a thin film of water in reducing the drag requirement. Many researchers [9-12] reported that friction is greatly modified by adhesion. Adhesion results primarily from moisture films that increase the perpendicular attractive forces between soil and the sliding surface of the tool. Adhesion may be reduced by using a material t h a t does not readily wet with water. The type and smoothness of the material on which the soil slides affect the adhesive properties [12-16]. The sources of adhesion are many and may include molecular, electrical, Coulomb and capillary forces. Of these, the most important source for off-road vehicles is capillary forces [17]. In the past, polytetrafluoroethylene (PTFE) and polyethylene, which have non-wettable characteristics, were used as coatings on mouldboard ploughs and other tools [12, 18]. Cooper and McCreery [9] found that when the lack of scouring is a problem, PTFE can improve scouring and that draft may be reduced by as much as 25%. Once applied to a surface, the material remains effective until it is worn away by the abrasive action of the soil. Gill and Vandenberg [19] pointed out that PTFE coating may be one of the factors which could eliminate the formation of soil bodies in front of tools. Wismer et al. [20] reported that covering a plough bottom with Teflon reduced the draft by 23% in soil where steel would not scour. However, Teflon showed very poor resistance to wear and abrasion. Many other attempts made to reduce friction and adhesion on a tool surface are listed by Koolen and Kuiper [12]. Salokhe and Gee-Clough [3, 4] studied the effect on soil adhesion of coating various materials on lug surfaces, floats and mouldboard ploughs. Results showed that the coating of such surfaces significantly affected the soil adhesion. They further reported that among the materials they used in their study, enamel coating was found to be the most promising. Salokhe et al. [5] studied the effect of coating materials on the forces required to pull floats in clay soil. They observed that by applying enamel coating, the drag force could be reduced by up to 50%. Suharno [21] studied the effect of enamel coating on the specific draft of a mouldboard plough in Bangkok clay soil. He reported that the overall reduction in the draft was in the range 8-23%. Salokhe et al. [22] studied the effect of surface coating on cage wheel lug forces in a laboratory soil bin and reported that at constant sinkage, slip and soil moisture content, the lug forces generated by a coated lug did not differ significantly from those generated by an uncoated lug. METHODOLOGY The experiments were conducted in a laboratory soil bin of 300 x 80 x 60 cm size (Fig. 1) [23]. Floats of 30 cm length and 15 cm width which were fabricated from mild
C O A T E D FLOATS IN DIFFERENT SOILS
5 •
50
175
300
~1
Plan Soil
- -
-
-
Soil bin Drum Electric motor Chain Sprocket Pulley
Load cells Floot
Side view
-- I~/~/lllll/ll///I,//I///I
/ i/lll.~////i//i///////i/i All dimensions in cm
Flo. 1. Schematic of experimental set up.
steel of 0.32 cm thickness were used for testing (Fig. 2). Two floats were coated with enamel and Teflon while the third was uncoated. The enamel coating was done in the same way as coating of home utensils. A solution was made from the enamel powder and was applied to the float and then it was baked in a furnace at about 700-800 °C. Teflon in liquid form was sprayed on the cleaned float and then it was baked. The uncoated float was cleaned and degreased. Three types of soil were used for testing, namely clay, loam and sandy. The average values of the moisture and cone index and other properties of these soils are listed in Tables 1-4.
FiG. 2. The floats used in the experiments: (a) enamel coated, (b) Teflon coated, (c) uncoated.
176
E. CANILLAS et al. TABLE1. PARTICLESIZEDISTRIBUTIONAND CONSISTENCYLIMITSOF THE THREESOILS Soil type
Soil characteristics Particle size distribution Clay (%) Silt (%) Sand (%) Consistency limits Liquid limit Plastic limit Plasticity index (%) Sticky limit (%)
TABLE2.
Moisture content (db) (%)
Clay
Loam
Sandy
56.1 35.4 8.5
16.3 36.1 47.6
00 2.8 97.2
47.2 23.5 23.7 34.1
32.5 20.3 10.2 23.8
m
m
m
COHESION AND ADHESION PROPERTIES OF CLAY SOIL
Cohesion properties
Adhesion properties
Cohesion (kPa)
Angle of internal friction (deg)
Material
Adhesion (kPa)
Soil material friction angle (deg)
21.2
23.4
24.1
27.8
19.4
19.6
33.6
15.2
16.3
40.4
8.3
11.2
62.4
--
--
Enamel Teflon Uncoated Enamel Teflon Uncoated Enamel Teflon Uncoated Enamel Teflon Uncoated Enamel Teflon Uncoated
1.4 2.1 2.6 2.0 2.2 4.4 4.3 5.1 5.8 4.8 5.6 6.3 ----
16.2 17.1 18.2 14.4 14.3 16.1 13.3 14.1 14.9 11.2 12.1 12.6 ----
Soil specific weight (kN/m 3)
Cone index (kPa)
18.2
1046
18.4
924
17.9
678
18.1
493
17.4
21
T h e floats were placed h o r i z o n t a l l y o n the soil surface a n d desired n o r m a l loads were m o u n t e d at a p o i n t b e h i n d the c e n t e r of gravity of the floats [24]. T h e forces r e q u i r e d to pull the floats a l o n g the soil b i n were m e a s u r e d . T h r e e types of floats were p u l l e d parallel in each test r u n by m e a n s of a trolley which was p u l l e d by a v a r i a b l e speed m o t o r . A c o n s t a n t p u l l i n g speed of 0.20 m/s was used to avoid the effect of i n e r t i a a n d h y d r o d y n a m i c forces [24]. T h r e e s t a n d a r d load cells h a v i n g a capacity of 1000 N were used to sense the force r e q u i r e m e n t for each float. A pulley was p r o v i d e d a n d p r o p e r l y a d j u s t e d to m a t c h with the height of the c e n t e r of the load cell. P r i o r to using, the load cells were calibrated. A strain amplifier was used to amplify the o u t p u t signals from the bridge circuit of the load cells. D a t a were r e c o r d e d o n a data logger a n d t r a n s f e r r e d to a m i c r o c o m p u t e r for f u r t h e r analysis.
177
COATED FLOATS IN DIFFERENT SOILS T A B L E 3. COHESION AND ADHESION PROPERTIES OF LOAM SOIL
Moisture content (db) (%)
Adhesion properties
Cohesion properties
Soil specific weight (kN/m 3)
Cone index (kPa)
Cohesion (kPa)
Angle of internal friction (deg)
Material
Adhesion (kPa)
Soil material friction angle (deg)
16.6
15.1
28.6
Enamel Teflon Uncoated
1.2 1.8 2.3
16.8 17.4 18.2
16.4
1134
21.3
12.6
23.9
Enamel Teflon Uncoated
1.5 2.2 3.8
15.1 15.6 16.2
16.8
897
24.0
8.2
18.4
Enamel Teflon Uncoated
3.8 4.5 4.8
12.3 12.9 13.8
16.0
758
27.6
7.4
14.2
Enamel Teflon Uncoated
4.6 5.1 6.1
9.6 10.4 11.0
16.1
562
Enamel Teflon Uncoated
----
----
15.6
20
36.1
TABLE 4. COHESION AND ADHESION PROPERTIES OF SANDY SOIL
Moisture content (db) (%)
Cohesion properties Cohesion (kPa)
Adhesion properties
Angle of internal friction (deg)
Material
Adhesion (kPa)
Soil material friction angle (deg)
Soil specific weight (kN/m 3)
Cone index (kPa)
0.7
0
37.4
Enamel Teflon Uncoated
0 0 0
18.7 20.9 22.6
14.4
621
5.1
0.121
35.3
Enamel Teflon Uncoated
0.013 0.023 0.029
18.2 20.4 22.3
14.8
671
9.4
0.133
34.6
Enamel Teflon Uncoated
0.018 0.032 0.037
18.1 20.2 22.1
14.7
642
12.2
0.135
33.2
Enamel Teflon Uncoated
0.021 0.034 0.038
17.9 20.0 21.8
14.6
651
13.8
0.143
33.4
Enamel Teflon Uncoated
0.024 0.033 0.038
17.6 19.7 21.7
14.7
592
RESULTS AND DISCUSSION
Performance of floats in clay soil F i g u r e 3 s h o w s t h e a v e r a g e d r a g f o r d i f f e r e n t f l o a t s a t v a r i o u s n o r r ~ a l l~-,~ ., , 21.2% moisture content. All floats had the same contact area and were subjected to
178
E. CANILLAS
et al.
55
Surface coating I
30
I~
I I
Enamel
I ~ Teflon
25
Uncoated
z o~ 20
~ 121
15
10
44 Normal load (N)
25
F I G . 3.
64
Average drag force of the floats in clay soil at 21.1% moisture content and different normal loads.
the same amount of sinkage. However, the sinkage was insignificant. It is evident from the figure that the enamel coated float produced the least drag force at any normal load. At 25 N normal load the enamel coated float produced 64% less drag force than the uncoated float. At 44 and 64 N normal loads it produced 59% less drag than the uncoated float. The better performance next to enamel was shown by the Teflon coated float. As the normal load increased the force required to pull all the floats also increased. The ratio, D/W, was calculated for all floats at different normal loads. It was found that for a particular float the ratio was almost the same as normal load increased. However, the uncoated float had higher ratio (0.5) while the enamel coated float had the lowest ratio (0.2) for a given normal load. The ratio for the Teflon coated float was 0.4. Figure 3 shows that the drag for the enamel coated float was significantly less than for the Teflon and uncoated floats. Figure 4 and 5 show the effect of soil moisture content on the average drag forces for each float at constant normal load. At 25 N normal load and 21.2% moisture content (Fig. 4), the average force required to pull the uncoated float was 2.75 and 1.42 times greater than the 6O
ISurfacecoatingI i Enamel
y 50
~
50
a
2O
/
A
~
I'-~- Teflon
I0
0
20
I
I
I
I
I
I
I
I
25
30
35
40
45
50
55
60
Moisture content (%)
FIG. 4. Average drag force for the floats at 25 N normal load in clay soil at different moisture contents.
COATED FLOATS IN DIFFERENT SOILS
179
140 [Surface coating
[--~[ --~-
120 I00 z
Enamel
Teflon
80
o
60
El
40 20 0 20
I
I
25
30
I
I
I
I
55 40 45 50 Moisture content {%)
I
I
55
60
FIG. 5. Average drag force for the floats at 64 N normal load in clay soil at different moisture contents.
force required for the enamel and Teflon coated floats, respectively. On the other hand, the drag for the Teflon coated float was 1.94 times greater than for the enamel coated float. Increasing the soil moisture from this level to 27.8% resulted in an increase of drag for all the floats. Such increase was very small for the Teflon coated float which had a relative increase of 7% compared to 33 and 52% for the uncoated and enamel coated floats, respectively. Considerable increase in draft force for all the floats was noticed when the soil moisture content increased to 33.6%. Compared with the dry soil condition, these forces were 3.73, 3.17 and 4.75 times greater for the uncoated, Teflon and enamel coated floats, respectively. Such increases might be intensified by the soil as it reached its plastic limit when maximum shearing stresses were expected to occur. At 40.4% moisture content, all floats produced their highest drag force. The drag values were 4.00, 4.53 and 7.33 times greater than in dry soil condition for the same floats, respectively. These increases in drag forces were due to a high clay soil adhesion at the float-soil interface (Table 2). Increasing the moisture content further to 62.4% resulted in a decrease in the drag force for all the floats. In general, the drag force for the floats in clay soil increased as the moisture content increased up to about 40% and further increase in moisture content caused a decrease in the drag force. At all moisture contents, the force required to pull the enamel coated float was the least compared to other floats. Increasing the normal load from 25 to 44 N, a similar trend of the drag force was observed. Figure 5 shows the drag force for the floats at 64 N normal load and at different moisture content. The trend of drag force for all the floats was similar to that observed for previous normal loads. As the moisture content increased the drag force increased but after attaining a peak value it dropped with an increase in moisture content. The variation in the drag force with moisture content can be well explained by the fact that in a dry soil condition, soil-metal friction is a significant component of drag force for tillage implements. As this component increases, the drag force likewise increases as soil changes properties with moisture content. In wet soil, soil-metal adhesion becomes a very significant factor. When the vector sum of the cohesive
180
E. C A N I L L A S et al.
forces is greater than the adhesive forces, soil-metal failure occurs. However, when the resultant of the adhesive forces is greater than the cohesive forces, soil-to-soil failure takes place. In the case of enamel and Teflon coated floats, less adhesive forces prevail compared to the uncoated float because of the smooth contact surface they provided. However, this argument may not hold good as the soil reaches its plastic and liquid limits. Scouring can be defined as the ability of material to allow the soil to flow over it without sticking on it. Scouring also reduces the drag of the floats. The statistical analysis by the 'F' test showed a significant difference in the drag force for the floats, The analysis of variance also showed significant effects of soil moisture content, normal loads and coating materials on the forces required to pull floats.
Performance of floats in loam soil Figure 6 shows the drag force for different floats at 16.6% moisture content in loam soil at different normal loads. The force required to pull enamel coated floats was much lower than for the Teflon and uncoated floats. At 25, 44 and 64 N normal loads the drag force for the enamel coated float was 46, 46 and 44% less than the uncoated float, respectively. At all normal loads the drag force for the enamel coated float was significantly lower than for the other two floats. Figure 7 shows the effect of loam soil moisture content on the drag force of different floats at 25 N normal load. The drag increased for all floats until the soil reached its plastic limit and then it decreased when soil moisture content increased further. The enamel coated float produced the least drag force at any moisture content. The drag force at 16.6% soil moisture content for the uncoated float was 1.9 times while for the Teflon coated float was 1.7 times greater than that of the drag of the enamel coated float. Increasing the soil moisture to 21.3% resulted in an increase in the drag forces for all floats. This increase might be caused by the increase in the adhesion between the soil and the working surfaces of the floats. At 24% soil moisture, a further increase in the drag forces was recorded. The uncoated float drag was 1.63 and 1.38 times greater than the drag force for the enamel and Teflon coated floats, respectively. Further increase in the soil moisture to 27.6% resulted in an increase in the drag
35 3025-
I Surface coating I~
Enamel
IMR Teflon
Uncoated
20-
c~
I05 i
25
I
44 Normal load (N)
I
64
FIG. 6. Average drag force of the floats in loam soil at 16.6% moisture content and different normal loads.
C O A T E D F L O A T S IN D I F F E R E N T SOILS
181
Surface coating I
--11{- Enamel
I I
Tel,on
I
4O Z
O
3O 2O 10 0 16
I
I
I
i
L
L
I
I
I
I
18
20
22
24
26
28
50
32
34
56
38
Moisture content (%)
FIG. 7. Average drag force for the floats at 25 N normal load in loam soil at different moisture contents.
forces. It was observed that the greatest drag forces for each float were produced at this soil moisture. Changing the normal load to 44 N resulted in the same trend of drag forces (Fig. 8). In the case of the uncoated float, the highest drag force was attained when the soil moisture was at 24%. It was noted that when working at 16.6% soil moisture, greater drag reduction was observed from the use of enamel instead of Teflon coating. The drag force for the uncoated float was almost equal to that of the Teflon coated float while it was 1.9 times greater than for the enamel coated float. As the soil moisture was increased to 21.3%, the drag forces for each float also increased. Increasing the soil moisture to 24% resulted in a considerable increase in the drag force for each float. It was observed that the drag force for the uncoated float was 1.7 and 1.8 times greater than the Teflon and enamel coated floats, respectively. At 27.6% soil moisture content, the drag force for the uncoated float decreased. Further increases were noticed in the case of the coated floats. It was noted that the highest drag forces were reached for both coated floats. This might be caused by a greater IOO
/ 8o -
z
Surface coating
~
I -x~ Enamel
i
/
Teflon
6o-
8
2O
0
16
I
I
I
18
20
22
I
L
I
I
24 26 28 50 Moisture content(%}
I
I
I
32
34
36
38
FIG. 8. Average drag force for the floats at 64 N normal load in loam soil at different moisture contents.
182
E. CANILLAS et al.
adhesion between the working surfaces of the floats and the soil coupled with the decrease in the cohesion between the soil particles which might have resulted in an increase of soil shearing. Increasing the soil moisture content to 36.1% resulted in a decrease in the drag force of all floats due to soil behaving like a liquid and offering less resistance to motion. At 64 N normal load, similar drag forces were noticed. The enamel coated float produced the least drag compared to the other two floats. The results of the analysis of variance revealed that the coating material, normal load and soil moisture content influenced the drag forces of floats considerably.
Performance of floats in sandy soil Figure 9 shows drag of different floats in dry soil (0.7% moisture content) at different normal loads. Even in very dry sandy soil the drag for the enamel coated float was much less than for the other floats. Compared to that of the uncoated float, the drag force for the enamel coated float at 25, 44 and 64 N normal loads was 45, 46 and 44% less, respectively. This was because the enamel coating could also reduce the friction at the float-soil interface significantly compared to the Teflon and uncoated floats. As the normal load increased the force required to pull all the floats also increased. The drag forces for each float at 25 N normal load and at varying soil moisture contents in sandy soil are shown in Fig. 10. It was observed that as the moisture content was increased, the drag force for each float also increased. The increase in drag forces with moisture content showed a different trend than that observed in clay and loam soil. At the lowest moisture content (0.7%), the reduction in the drag was about 45 and 16% for the enamel and Teflon coated floats, respectively, compared to the uncoated float. In this condition, the sand was very dry, and considering that most sandy soils are usually predominantly frictional, these results showed that enamel coating was still a promising material for reducing the soil-metal friction even in a sandy soil. The drag forces gradually increased as the soil moisture was increased up to 13.8%, which was considered as the saturated condition for this particular type of soil. It can be clearly noticed that, in these conditions, compared to the uncoated float the relative drag reduction ranged from 28 to 45% by the use of enamel coated floats. At 35
Surface cooting 30
Enamel I~
25
Teflon
17ff3 Uncoated
20
o= o
15
g c~
IO
I
25
44 Normal l o a d ( N )
64
FIG. 9. Average drag force of the floats in sandy soil at 0.70% moisture content and different normal loads.
COATED FLOATS IN DIFFERENT SOILS
183
20
15
E3 Surface coating l 5
-]I[-- Enamel -.~ Teflon
I
-[3- Uncoated 0
I I
0
i 2
i :3
I 4
I 5
I 6
~ 7
I 8
i 9
I0
I II
k 12
L I.%
14
Moisture content (%)
F~6.10. Average drag force for the floats at 25 N normal load in sandy soil at different moisture contents.
44 N normal load and in a dry condition, compared to the uncoated float, reductions of 46 and 16% in drag force for the enamel and Teflon coated floats, respectively were recorded. At 64 N normal load the reduction in the drag force was in the range 27-44% for the enamel coated float. When tested statistically, it was found that in sandy soil, normal load, soil moisture content and the coating materials had a significant effect on the drag of the floats at 99% level of significance. Figure 11 reveals the average percentage drag reduction by enamel coating on the float compared to the uncoated float in different soils and moisture contents at 25 N normal load. In all cases it was observed that an increase in moisture content caused a decrease in the benefits derived by enamel coating on the floats. In sandy soil, the overall reduction in the drag was from 45 to 28% when the moisture content increased from 0.7 to 13.8%. In loam soil the percentage reduction in the drag due to enamel poating was from 46 to 22% when the moisture content increased from 16.6 to 36.1%. In clay soil the percentage drag reduction by enamel coating compared to the uncoated changed from 64% at 21.2% moisture content to 20% at 62.4% moisture content. 70 Soil type HD- Sandy soit -<3- Loam soil
60
= .o
50 40
E3
30
o~ 20 I0 0
0
I
L
I0
20
I
I
50 40 Moisture content (%)
~
I
50
60
70
F~G. 11. Average percentage drag reduction for enamel coated float compared to uncoated float in different soils.
184
E, CANILLAS et al. CONCLUSIONS
T h e p e r f o r m a n c e o f the e n a m e l c o a t e d float was f o u n d to be s u p e r i o r to that of T e f l o n a n d u n c o a t e d floats in all soils a n d w o r k i n g c o n d i t i o n s t e s t e d in this study. F o r all floats in clay a n d l o a m soil, d r a g force i n c r e a s e d with i n c r e a s e in m o i s t u r e c o n t e n t up to the plastic limit a n d a f u r t h e r i n c r e a s e in m o i s t u r e c o n t e n t c a u s e d d e c r e a s e in the d r a g force. In s a n d y soil, h o w e v e r , t h e d r a g force i n c r e a s e d with t h e soil m o i s t u r e c o n t e n t . T h e effect o f t h e m o i s t u r e c o n t e n t , c o a t i n g a n d n o r m a l l o a d s o n the d r a g forces was f o u n d to b e statistically significant at a 99% level o f significance. D e p e n d i n g o n the n o r m a l l o a d a n d soil m o i s t u r e c o n t e n t , an e n a m e l c o a t i n g o n the float r e d u c e d the d r a g force by 4 to 64% in a clay soil, 16 to 46% in l o a m soil a n d by 26 to 45% in s a n d y soil. T h e significant d i f f e r e n c e in d r a g force for d i f f e r e n t floats c o u l d be a t t r i b u t e d to t h e d i f f e r e n c e s in the a d h e s i o n c h a r a c t e r i s t i c s of the c o a t i n g m a t e r i a l s a n d the s o i l - m a t e r i a l friction b e t w e e n the soil a n d the floats. T h e e n a m e l c o a t e d floats s h o w e d e x c e l l e n t w e a r r e s i s t a n c e while the o t h e r floats s h o w e d signs of w e a r in d r y soil c o n d i t i o n s . In a n o t h e r e x p e r i m e n t by S a l o k h e et al. [25] e n a m e l c o a t i n g has s h o w n e x c e l l e n t w e a r r e s i s t a n c e . T h e results of this s t u d y clearly r e v e a l e d that e n a m e l c o a t i n g p e r f o r m s well n o t o n l y in clay soil b u t e q u a l l y well in l o a m a n d s a n d y soil. T h e s e results a r e v e r y p r o m i s i n g a n d s h o w t h a t e n a m e l c o a t e d i m p l e m e n t s o r tools can b e u s e d to a d v a n t a g e in a wide r a n g e o f soil types.
REFERENCES [1] R. A. KEPNER, R. BAINER and E. L. BARGER, Principles of Farm Machinery, 3rd Edition. AVI Publishing Company, Westport, Connecticut (1982). [2] J. R. O'CALLAOHANand J. G. McCoy, The handling of soils by mouldboard ploughs. J. agric. Engng Res. 10(1) (1965). [3] V. M. SALOKHEand D. GEE-CLOuGH, Studies on effect of lug surface coating on soil adhesion of cage wheel lugs. Proc. 9th Int. Conf. 1STVS, Barcelona, pp. 389-369 (1987). [4] V. M. SALOKHEand D. GEE-CLouGH, Coating of cage wheel lugs to reduce soil adhesion. J. agric. Engng Res. 41(3), 201-210 (1988) [5] V. M. SALOKHE, D. GEE-CLOuG, and A. I. MuFn, Performance evaluation of an enamel coated mouldboard plough. Proc. Int. Congress agric. Engng, Dublin, pp. 1633-1638 (1989). [6] F. A. KUMER and M. L. NICHOLS, The dynamic properties of soil: a study of the nature of physical forces governing the adhesion between soil and metal surface. Agric. Engng 19, 73-78 (1938)• [7] W. SOEHNE, Suiting the plough body shape to higher speeds. GrundL landtech. 12, 51-62 (National Institute of Agricultrural Engineering Translation no. 101) (1960). [8] D. GEE-CLouGH, Special problem of wetland traction and flotation. J. agric. Engng Res. 32(3), 227-229 (1985). [9] A. W. COOPER and W. F. MCCREERY, Plastic surfaces for tillage tools. ASAE Paper No.61-649 (1961). [10] P. L. DANO, The influence of soil conditions on the effectiveness of electro-osmosis and Teflon in reducing friction. Auburn University M.S. Thesis (Unpublished) (1961). [11] W. R. Fox and L. W. BOCKHOP, Characteristics of a Teflon-covered simple tillage tool. Trans. ASAE 8(2), 227-229 (1965). [12] A. J. KOOLENand H. KUIPER, Agricultural Soil Mechanics. Springer, Berlin (1983). [13] F. R. BOWDENand D. TABOR, Friction and Lubrication. John Wiley, New York (1960). [14] G. SPooR, Design of soil engaging implements. Farm Machinery Design Eng (September 1969). [15] M. L. NICHOLS, The dynamic properties of soil (II). Soil metal friction. Agric. Engng 12, 321-324 (1931). [16] J. G. POTYONDY, Skin friction various soils and construction material. Geotechnique 11(4), 339-353 (1961). [17] A. D. ZIMON,Adhesion of Dust and Powder. Plenum Press, New York (1969). {18] R. D. PILLSBURY,Application of fluorocarbon resins in farm equipment. Agric. Engng 41, 802-803, 725, 826 (1961). [19] W. R. GILL and G. E. VANDERBERG, Soil Dynamics in Tillage and Traction. Agriculture Handbook no. 316, USDA, Washington (1968).
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[20] R. D. WISMER, E. L. WEGSCHEID,H. L. LuTrf and B. E. RANING, Energy application in tillage and earth moving. Soc. Auto. Engrs 77, 2486-2496 (1968). [21] SUHARNO, Performance evaluation of an enamel coated moudboard plough. Asian Inst. Techn. M. Eng. Thesis no. AE-89-14 (unpublished) (1989). [22] V. M. SALOKHE, D. GEE-CLOUGH and S. MANSOOR, Studies on effect of surface coating on forces produced by cage wheel lugs in wet clay soil. J. Terramechanics 27(2), 145-157 (1990a). [23] E. CANILLAS,Performance of coated floats in different soils. Asian Inst. Techn. M. Eng. Thesis no. AE-90-3 (unpublished) (1990). [24] N. G. SHAH, Study of float devices for wet land machinery. Asian Inst. Techn. M. Eng. Thesis no. AE-80-20 (unpublished) (1980). [25] V. M. SALOKHE, D. GEE-CLOUGH and P. TAMTOMO, Wear testing of enamel coating rings. Soil Tillage Res. 21(1/2), 121-131 (1990b).