The B.F.T Abrasion Testing Machine
In includes a series of mechanisms to abrade textile materials which provide numerical results which can be correlated with serviceability.
Special Features of this instrument:
- The end-point of the test is determined automatically by the machine. It stops automatically when the end-point is reached.
- The abradant used in the various accessories is made of special steel whose abrasive characteristics remain constant and are capable of being reproduced to any specification.
- The machine is sturdily built and capable of being run smoothly at high speeds for a long time.
- The result of tests on the machine can be analyzed and expressed numerically and fabrics may be ranked in order of merit.
Construction:
The mechanical parts are mounted on a rigid platform ‘P’. A solid aluminum carriage ‘C’ is given reciprocated motion with a stroke of 1½” at 700 rpm which is achieved by a crank and connecting rod mechanism. A six-digit counter records the number of cycles made. The head ‘H’ is mounted over the top of the reciprocating carriage ‘C’ and moves vertically due to parallel link motion. Counter poise weights are employed, so that with no weights on the spigot ‘S’ the movement is just in balance; hence known vertical loading can be obtained by adding the required weights to the spigot. The control unit and motor are mounted below the platform.
Three types of test are made and three sets of interchangeable accessories are provided with the instrument.
a. Flex Test:
For flex testing the abradant is a flex plate. The flex plate is a stainless-steel plate about 0.037 inch thick with one edge tapered off and rounded to 0.017” dia.
This plate is given a reciprocating motion. Tension is applied to the test specimen by the weight on a bell crank lever acting through a chain link.
The test sample is 5” long and 1” wide. The sample is secured at one end over a row of stenter pins on the carriage and led round the radiused edge of the flex plate and the free end is then secured over the stenter pins.
A load of 4 lb is added to the spigot S and a 2 lb weight to the bell crank lever, thus a 2:1 velocity ratio causes the tension in the specimen to be 4 lb.
When the machine is switched on the reciprocating of the carriage causes the fabric to be repeatedly pulled back and forth round the edge of the flex plate and continuous flexing is achieved. Eventually the fabric breaks and a switch is operated, automatically stopping the machine. The number of cycles is read from the counter and recorded. The mean of five tests is taken- warp way, weft way, or in both direction if necessary.
Since the number of cycles obtained is quite high, the mean value is divided by 1000 for easy handling of the result.
Flex Result, P = Mean value of 5 tests / 1000
b. Ball Toughness:
In this test a cover plate with a hardened tool-steel strip is clipped on to the top of the carriage C. The test strip is mounted over this steel plate and secured by stenter pins on either side of the carriage. The abradant is (3/16)” ball bearing in a special holder which is pushed home into the upper head H.
A load of 1.5 lb is added to the spigot. The sample will be 6” × 1” in size. If the warp ball toughness is to be tested, the long side of the specimen will be parallel to the weft, so that the ball runs across the warp threads.
With the moto running, the carriage reciprocates beneath the ball and in time the ball penetrates the fabric and then contacts the hardened strip. When this happens a small current flow, small enough to avoid any chance of sparking and turn switches the machine off.
Five tests are carried out for warp & weft and mean values are recorded. The number of cycles is normalized by a factor 10-2 and the ball toughness B is calculated as
Ball toughness, B = Mean of 5 tests / 100
The ball penetration tests depend to certain extent on the fabric structure but is mostly related to the toughness or brittleness of the individual fibres. A treatment which increases fibre brittleness reduces the B value considerably. Lubrication has a comparatively small effect on B. Increase of lubrication leads to decrease the B value a little.
c. Flat Abrasion
The abradant used in the flat abrasion test is a stainless-steel gauze in a special holder which is fixed to the upper head by springs. An extra counterpoise weight is clipped to the rear end of the upper link of the parallel motion in order to balance the mass of the gauze holder. The test specimen is stretched over a resilient pad of conducting material and clipped to the carriage.
A 2 lb load is added to the spigot S. After a certain amount of rubbing the steel gauze contacts the pad, a current flow, and the machine is switched off automatically.
So, By normalizing,
Flat Resistance, F = Mean of five values / 1000
Credit:
Books: Principle of Textile Testing by J.E. Booth
and Textile Testing by P. Angappan & R. Gopalakirishnan
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