Use, maintenance and practice teaching construction of M-2 pre-grinding machine

Zong Bin Wang Erping Wei Jianzhong Beijing University of Technology Beijing 100022

Abstract: The standardized use of M-2 pre-grinding machine can improve work efficiency and ensure operation safety. Carrying out equipment maintenance in time to solve the problems of noise, jitter and water seepage is not only conducive to the effective development of the course operation in the practical link, but also the specific practice of "green experiment".
Keywords: M-2 pre-grinding machine; operating specifications; maintenance; green experiment

The pre-grinding machine is a kind of conventional equipment in the metallographic examination. Among them, the M-2 pre-grinding machine is a model with a relatively large quantity (as shown in Figure 1). This type of pre-grinding machine is the one we configure in the practical teaching link of "metallographic sample preparation experiment" for undergraduates. The experience of using and maintaining it is summarized here for the reference of interested teachers.

1. Use of M-2 pre-grinding machine

1. Operating Specifications

Our laboratory purchased the "Sailing Brand" water sandpaper produced in Tianjin, the specification is 235 × 275mm; the sandpaper combination of the corresponding specification can be selected according to the roughness of the grinding surface of the sample. In the case of specific consumables, refer to the instruction manual of the equipment, especially in combination with our own practice, to formulate the following M-2 pre-grinding machine operation specifications.

(1) Cut out the appropriate diameter and suitable round sandpaper (diameter 205mm) according to the size of the model or the grinding disc of the pre-mill. (2) Remove the water retaining plate, turn on the water source, fill the grinding disc with water, and then turn off the water source. Put the sandpaper into the card and cover the water tray. Do not rub the water-retaining disc against the grinding disc. It should maintain a distance of about 10 mm to facilitate the cooling water to wrap the grinding product and throw it out of the grinding disc. (3) Turn on (turn on) the power, the grinding disc rotates, the water under the sandpaper is thrown out, and the atmosphere presses (absorbs) the sandpaper on the grinding disc. (4) Turn on the faucet to form a continuous water flow (it should not be too large to save water); do not use the water flow control switch on the device. (5) During the polishing process, press the grinding surface of the sample evenly on the sandpaper to keep the sample as smooth as possible. When the surface of the sample is flat and shows a uniform direction of scratches, the polishing of this sandpaper can be stopped. Turn off the water source and power supply, remove the sandpaper on the grinding disc, turn on the water source to clean the sand and abrasive debris on the grinding disc, and then replace the fine-grade sandpaper to continue grinding. (6) At the end of use, remove the sandpaper from the grinding disc; then, dry the disc area water. It is not necessary to cover the lid, which is conducive to the drying of the disk surface; clean the surrounding environment and restore it to its original state.

It should be noted that in many professional books and product manuals of the M-2 pre-grinding machine, the text that introduces the use of the pre-grinding machine will mention that: under the action of the centrifugal force of the grinding disc, the water under the sandpaper is thrown out of the disc outer. The expression "centrifugal force" appearing here is wrong. It should be centrifugal motion without centrifugal force; this is a wrong understanding of basic physical concepts.

Standard operation can improve efficiency, and at the same time, safety needs more attention. There are indeed safety issues in the use of pre-grinding machines, but there will never be a so-called "injury or disability". Of course, this requires some preliminary work in the design of the laboratory and the use of the pre-grinding machine, which can be completely avoided. First, under normal circumstances, the flexibility of the operator's right hand is higher than that of the left hand, so the rotation direction of the grinding disc is adjusted to rotate counterclockwise. During the polishing operation of the sample, the operator is required to be located on the right side of the grinding disc; in this way, the specimen will fly forward in the case of an accidental missed hand, and will not hurt the operator. In addition, the placement of the pre-grinding machine should be placed against the wall, and should be placed against the wall; to avoid the test piece flying out, injuring the operator on the opposite side. With more than 20 years of work experience, the author has seriously considered these issues, and has never seen an incident in which a test piece flew out and touched the person. Of course, depending on the situation, 1 or 2 clockwise pre-mills will be reserved to facilitate the use of left-handers. See Figure 2 for the equipment shelving in our laboratory.

2. Problems during use

In the process of using the pre-grinding machine, we had a running accident. The reason is that only the cooling system switch on the pre-mill is turned off, and the faucet connected to the cooling water system is forgotten to be turned off. In this way, the municipal water pressure causes the original hose connection in the equipment box to stretch (the connection of the internal water pipe is not considered for tightening). This is a lesson for us, so this factor was taken into account when formulating the operating regulations; it is not allowed to turn off the cooling system switch on the pre-mill, and the tap switch must be used. In addition, the original aging rubber hose was replaced with a plastic tube reinforced with a braided mesh, which was fastened by means of a hoop (the clamped area of ​​the hoop is large and stable, and the interface is well protected).

During the short-term use of the M-2 pre-grinding machine, the operation of all aspects of the equipment is satisfactory. With the increase of time and frequency of use (we not only have teaching tasks, but also relevant practice links for undergraduate and graduate graduate thesis), usually after 2 years, the noise of the equipment increases significantly; at the same time, the vertical jitter of the grinding disc is also Exacerbated. In addition, leaks in the gaps in the rotatable joints of the cooling system are constantly emerging; the situation is getting worse year by year. The metallographic sample preparation laboratory has 10 pre-grinding machines, which are turned on at the same time, and the noise in the room is deafening. It not only affects the communication between teachers and classmates, but also is not conducive to the concentration of students and it is easy to get tired; it even affects the work of the surrounding laboratory staff. In addition, the vertical vibration of the grinding disc also affects students to better master the technology and improve efficiency during the experiment. The water leakage phenomenon causes water accumulation on the countertop and ground, which is wasteful and unsafe. Taking effective maintenance measures is a necessary consideration for the construction of practical teaching links.

2. Maintenance

1. Solution to the leakage of cooling system gap

As the use time increases, the original seals in the cooling water system age and wear out. Under the municipal water supply pressure of the tap water, water easily overflows from the contact gap, which reduces the effective cooling water flow and also causes water The location of waste and water leakage is shown in Figure 3. The part framed by the dotted line in FIG. 3 is the place where water leaks easily, and its simple internal structure is shown in FIG. 4.

At the position of the seal 1, we select an old vacuum seal ring of suitable size, and the outlet pipe is pressed down tightly. As for the position of the seal 2, a common desktop rubber or thick latex tube is used. According to the size of the fitting, a sealing gasket of an appropriate size is cut, and the inner diameter is slightly smaller than the outer diameter of the water pipe, so as to fit tightly. In this way, the components A and C will have a certain elastic seal 2 closer to the water pipe during the tightening process, which helps prevent water leakage. In this way, the problem is solved in a simple form. We have specially prepared a small tool for the problem of water leakage, which is convenient for intercepting the sealing rubber; in the future, the problem of water leakage will be solved at any time (as shown in Figure 5).

2. Resolution of noise and jitter

The vulnerable parts in the pre-grinding machine include bearings and V-belts. Bearings need regular maintenance, maintenance, oiling, and grease replacement during use. At the same time, the disassembly and installation of bearings require special tools and techniques, otherwise they will directly damage the bearings. The gradually increased noise and jitter of the pre-grinding machine are caused by the imbalance caused by the wear of many parts of the bearing for a long time. In different parts of the whole equipment, a total of 8 203, 204 single-centred radial ball bearings need to be replaced. As for the triangle belt (O type 1120), according to our use, it can be used normally for more than 10 years (the frequency of use by schools and scientific research institutions).

At the same time, the original bearing is a type without an envelope, which requires regular maintenance, and has higher requirements on the use environment. We use new envelope type motor special bearings (produced by Harbin Bearing Factory) for maintenance, which can avoid maintenance during the life of the bearing; the appearance of the two types of bearings is shown in Figure 6.

3. Cleanup of sediment

During maintenance, the device panel must be opened. The screws fixed on the panel and the base are easy to rust, and some screws must be removed with an electric drill before they can be removed; therefore, it is usually not easy to clean the internal deposits. The timing of maintenance can be used to incidentally clean up the metal debris deposited in the pre-mill for a long time; no special cleaning work is required.

3. Conclusion

The "greening" of experiments is the trend of the development of experiments in colleges and universities; there are many chemistry and biology departments who first proposed such ideas. However, other disciplines can also absorb its essence and actively apply it to the practice teaching process of various specialties. The noise pollution and waste of water and electricity resources during the use of the pre-grinding machine can be eliminated or reduced as much as possible through our timely maintenance. It should also be considered to practice the "green" concept in detail.

References [1] Han Dewei, Zhang Jianxin. Metallographic sample preparation and display technology [M]. Hunan: Central South University Press, 2005
[2] Shanghai Daily Motor Factory. M-2 metallographic sample pre-grinding machine product manual [M]. Shanghai: Shanghai Daily Motor Factory, 2002
[3] Cheng Shouzhu, Jiang Zhiyong. General Physics [M]. Beijing: Higher Education Press, 1982
[4] Cai Yulian, Jing Weiwei. Development of polishing fixture for metallographic specimens [J]. Journal of Jilin Agricultural University, 1984, 6 (4): 33 ～ 35
[5] Ying Jinfang. Thinking and practice of maintenance frequency of double-sided sealed ball bearings for small motors [J]. Small and medium motors, 1999, 41 (4): 40 ～ 41
[6] Wang Lizhi. The application of rolling bearings [J]. Science and Technology Information, 2007, 5 (6): 83 ~ 84
[7] Jiang Yuping. On the greening of chemistry experiments in colleges and universities [J]. Experimental Technology and Management, 2005, 22 (7): 94 ～ 97

* This article is the 2007 Educational Teaching Research Project of Beijing University of Technology (2007-B-07), research on the connotative development of optical analysis experiment teaching module.

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