Central Research Laboratories
January 11, 1988
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Tests were conducted at a major tannery in Maine, U.S.A. to evaluate mechanical slicking vs. hand slicking during paste drying. The mechanical slicker, known as the Power Slicker, developed by Central Research Laboratories (CRL), was used during the test. The tests were set up to observe what differences occur between power slicked and hand slicked hides in the areas of yield, thickness, residual paste, and neck wrinkles on 2.3 mm leather. Extensive controls were used on 200 matched sides. Evaluation of the data revealed that mechanical slicking has significant advantages over hand slicking. |
CRL, the manufacturer of the Power Slicker, sought reliable, unbiased test data to verify the effects of mechanical vs. hand slicking. CRL contacted the Leather Industries of America (LIA) Research Laboratories for input on how such data could be obtained. The cooperating tannery in Maine agreed to run the tests using the controls suggested by the LIA Laboratory in addition to those already in place at the tannery.
A total of 200 matched sides were used (2 lots of 100 sides each.) The tannery started with 200 whole hides which were split to 2.5 mm, shaved to 2.3 mm, and sided. Each side in each lot was given a number from 1 to 100. The sides were picked randomly with an equal number of lefts and rights in each lot. All drying, conditioning, and finishing were identical with two exceptions:
The tests were set up to measure yield, thickness, residual paste, and neck wrinkles. All sides were trimmed in the blue and at no other time in the process. Area measurements were taken in the blue, after setting out, after paste drying, after conditioning, and prior to final sort and trim. The thickness was measured in five places:
In addition, each side was visually inspected for residual paste and neck wrinkles. The inspections were done by one person who was unaware which side was test or control.
Several additional controls were provided to insure the most accurate results possible:
| Hand | Power | |
|---|---|---|
| First half hour of shift | 34 sides | 34 sides |
| Middle half hour of shift | 32 sides | 32 sides |
| Last half hour of shift | 34 sides | 34 sides |
For the purpose of presentation, we will discuss the tests in four components:
The figure below shows the total square footage of each lot measured:
Following are the yield results for each lot.
| Process Step | Area Measurements (sq. ft.) | Yield | ||
|---|---|---|---|---|
| Power Slicked | Hand Slicked | Power Slicked | Hand Slicked | |
| In the blue | 2033.5 | 2047.8 | N/A | N/A |
| After setting out | 2072.0 | 2083.5 | 1.9% | 1.7% |
| After paste drying | 2139.7 | 2104.0 | 5.2% | 2.7% |
| In the crust | 2040.5 | 2002.5 | 0.3% | -2.2% |
| Prior to final sort and trim |
1972.8 | 1937.8 | -3.0% | -5.4% |
The final result shows a 2.4% improvement in yield of the finished product using the mechanical slicker. Evaluation of the data reveals most of the yield gain was achieved during the slicking operation (e.g. 5.2% for power slicking vs. 2.7% for hand slicking.)
Residual paste results were measured as Good, Fair, and Poor using the following guide:
The results are shown in the table below.
| Rating | Power Slicked | Hand Slicked |
|---|---|---|
| Good | 62% | 17% |
| Fair | 31% | 34% |
| Poor | 7% | 49% |
The power slicked leather ranked in the Good or Fair range for 93% of the test lot and in the Poor range only 7%. The hand slicked leather ranked in the Poor range for 49% of the test lot.
Neck wrinkles were rated as:
The results are shown in the table below.
| Rating | Power Slicked | Hand Slicked |
|---|---|---|
| 0.0 | 26% | 9% |
| 0.2 | 57% | 65% |
| 0.4 | 17% | 26% |
Test results indicate that neck wrinkles were eliminated on 17% more of the power slicked sides. The power slicked leather had 8% fewer neck wrinkles in the 50-75 mm range and 9% less in the 75-125 mm range.
The final test was thickness as measured in the neck, bend, butt, belly, and rear shank. The measurements were taken to 0.0 mm. The following data shows the average thickness measured in each lot (in millimeters.)
| Neck | Bend | Butt | Belly | Rear Shank | |
|---|---|---|---|---|---|
| Hand | 2.48 | 2.56 | 2.50 | 2.50 | 2.44 |
| Power | 2.41 | 2.52 | 2.47 | 2.47 | 2.41 |
It is interesting to note that the thinnest section for the power slicked leather is the neck, while the thinnest area for hand slicked leather is the rear shank. As can be seen from the data, all areas measured are thinner for the power slicked lot as compared to the hand slicked lot.
Yield - The test results show power slicking increased the yield 2.4% over hand slicking. In fact, the test lot started with less square footage than did the control lot, but ended with more.
Residual Paste - Power slicking significantly reduces paste marks.
Neck Wrinkles - Power slicking reduces neck wrinkles.
Thickness - There is a decrease in thickness with a corresponding increase in yield.
One possible reason for the thinnest area of the hand slicked lot being the rear shank is that area of the side is easy to slick because of the downward strokes. The Power Slicker applies constant pressure whether up or down.
Similar controlled tests were performed at two other major Midwest U.S. tanneries on different weights of leather. The results were similar with the exception of achieving higher increases in yield. The benefits of power slicking may vary from tannery to tannery depending on:
With experience, these variables can be adjusted to optimize yield and quality.
CRL would like to thank the cooperating tannery in Maine, U.S.A., the Leather Industries of America Research Laboratory, and Mr. Frank Rutland for their contributions to this report. CRL would also like to thank the cooperating tannery in Maine as well as the two Midwest tanneries for sharing their test data and their continued support in the development of the Power Slicker.