1) This handsheet making procedure is based on Tappi Method T 205.
2) The handsheets which will eventually be tested require minimal fines loss. This is an issue especially when using TMP and CTMP, as well as HW pulps. Hence the handsheets are made on a handsheet maker equipped with a whitewater recirculation system (see figure 16 and 17).
Figure 16: On the left, the entire handsheet maker in PPC; on the right, the whitewater recirculation system. Valve 1: whitewater to refill cylinder; Valve 2: whitewater bypass for agitation in the reservoir; Valve 3: fresh water to refill cylinder or prime the funnel under the screen.
Figure 17: Directions of water flows of the whitewater recirculation loop. j: Using fresh water to fill up the cylinder while producing whitewater from the first three handsheets; k: Using whitewater to fill up cylinder to make correction (three) and testing (ten) handsheets; l: ready to drain cylinder to form handsheet or while idling, keep the bypass on all the time to agitate whitewater in reservoir.
3) Ensure that the lower runoff valve of reservoir is closed and the whole handsheet maker is clean. Fill the cylinder on the handsheet maker to about a quarter of the way up with fresh water and then quantitatively transfer the suspension (~ 400 g) into the cylinder. Fill the cylinder to the engraved line. Take a piece of blotting paper and wet it completely with a squirt bottle. This piece will be used for the handsheet making process for your entire sample.
4) Place the perforated plunger into the cylinder (see figure 18) and make sure the bottom multi-holed plate is submerged. Hold the handles for guidance but let gravity pull the plunger. The plunger can only go down to a certain extent and when it reaches that limit, pull it up at the same speed gravity was pulling it down. Avoid bubble formation by not letting the bottom of the 4 fins leave the water. Definitely do not let the bottom multi-holed plate leave the water. Repeat this down and up motion another 4 times, the 5 repetitions should take around 5 ± 1s for each movement.
Figure 18: On the left, insert the plunger into the cylinder slowly; on the middle, the lower position of the plunger; on the right, the higher position of plunger.
5) Now repeat the motion one final time, but this time take 6 seconds. Slowly remove the plunger without rotation. Wait 5 seconds, then push down the lever to drain the cylinder through the mesh at the bottom.
6) The moment the handsheet on the bottom breaks the surface of the water, pull up the lever to stop the suction. Note: The over-aspirated TMP handsheets are difficult to be lifted and may have lower fines content. Place a new, dry piece of blotter on top of the handsheet gently, making sure that the handsheet is centered (see figure 19, do this visually before you drop the blotter onto the handsheet). Note: The moment the pulp touches the blotting paper, you must let go, and make no further adjustments.
7) Place the wet blotter on top of the dry blotter. Place the metal couching disc on the blotter (centered over the handsheet, see figure 19). Take the coucher, the big metal rolling pin, and carefully place it in the middle of the couching disc (figure 20). Do not drop or apply extra pressure downwards on the pin. A barely visible indentation across the handsheet is created if you drop the pin. This over-pressed area (it is still difficult to identify it while performing Handsheet Inspections) will eventually cause low strength of the defected handsheet. The handsheets must be couched with a specific force, which is precisely supplied through the weight of the rolling pin. Note: the couching disc is larger than the pressing disc.
Figure 19: On the left, handsheet is formed; in the middle, place the first dry blotter on top of handsheet; on the right, well centered blotters and couching disc on top of handsheet.
Figure 20: On the left, the couching pin is gently placed at the middle of couching disc; in the middle, rolling couching pin with palms up; or, on the right, rolling couching pin with circles formed by thumb and index fingers.
8) Let the pin roll freely on your palms or finger circles while pushing the pin back and forth. Roll the pin 5 times: First roll starts from the middle, up to the top, down to past middle to the bottom, and up to the middle again. Apply five rolls to couching disk. Note: Do not let the pin roll on or off the edge of the disc, keep the pin a minimum of 1” away from the edge while rolling (see middle picture of figure 20).
9) Take away the pin, and hold the corner of the blotting papers. Turn it quickly like turning the page of a book. This will lift the handsheet off the mesh. The handsheet should be uniform, have no deformations and be very smooth (see figure 21). There should be minimal material left on the mesh.
10) Peel off the wet blotter and the couching disc. Take the handsheet and blotter and carefully label the actual handsheet with the special indelible pencil. It is ideal to label on the edge of the handsheet. If the handsheet has a very slight deformation near the edge, you can still use it, just label on or near the deformed spot. Gently rub off the fibers with water that are left on the 200 mesh. Close the cylinder. The first few handsheets are not valid for testing. They can be tested for gaining practice, however.
Figure 21: On the left, ready to lift the handsheet; in the middle, handsheet is lifted with no defect visible; on the right, use indelible pencil to mark the handsheet.
11) Repeat the procedure three times to collect whitewater to reservoir, and discard these blotters and handsheets at this stage.
12) Turn pump on and open valves 1 and 2 to refill the cylinder and agitate the reservoir. Repeat the same handsheet making procedure as described from step 4) to 9) to make three basis weight correction handsheets. Put these three handsheets with blotters to speed dryer. Peel handsheets off the blotters ten minutes later and leave the handsheets in the dryer until constant weight is reached (see figure 22).
Figure 22: Basis weight correction handsheets are being dried in speed dryer.
13) The target weight for a handsheet is 1.20 ± 0.4 g (OD). You need to calculate how much suspension equates to 1.20 g of OD weight pulp. The consistency of the handsheet making suspension has been determined from the freeness test.
The “X g” suspension tells you the ideal weight of suspension you must add to get 1.20 g of OD pulp. But never make handsheets simply based on this ideal number since there will be a lot of fines loss that renders the basis weight drifts away significantly. For example, the consistency in freeness test is 0.294% of suspension; the result of calculation of X is 408.16 g.
So for 408.16 g we must take at least three samples of 410.00 g to make handsheets and collect whitewaters into reservoir. These three handsheets will be discarded. Take three more samples of 410.00 g to make handsheets with whitewater recirculation. Their OD weights (use speed dryer) will be used to correct the yield loss hence to reach the targeted 1.2 g per handsheet.
The “Y g” suspension tells you the corrected weight of suspension you must add to get 1.20 g of OD pulp per handsheet. For example, the averaged weight of three handsheets (with whitewater recirculation) is 1.166 g (from 410 g of suspension). The result of Y is 421.96 g. We will take 422 g of suspension to make ten handsheets of 1.2 g per sheet (60 g/m2 basis weight).
14) The fines content in the handsheets normally stabilizes when there is about ~seven to eight handsheets worth of fines in the reservoir. You can observe the gradual increase of OD weight of handsheets from the first one onward, then it approaches a plateau at the seventh or eighth handsheet. But it still varies depends on the type of pulp. In other words, the machine needs you to run about 3000 g of suspension through the system first before you can make handsheets for valid testing. It is a time and material consuming procedure at this stage. We normally make three correction handsheets to save the time and materials, besides the suspension cannot sit still for longer than thirty minutes while waiting for the OD weight of correction handsheets. The averaged number is used to make the final ten handsheets following the same step by step procedure described above.
