复合材料与工程专业毕业设计外文文献翻译.doc

济南大学毕业设计外文资料翻译

毕业设计外文资料翻译

题 目 POLISHING OF CERAMIC TILES
抛光瓷砖
学 院 材料科学与工程
专 业 复合材料与工程
班 级 复材0802
学 生
学 号 20080103114
指导教师

二〇一二年三月二十八日

MATERIALS AND MANUFACTURING PROCESSES, 17(3), 401–413 (2002)

POLISHING OF CERAMIC TILES

C. Y. Wang,* X. Wei, and H. Yuan

Institute of Manufacturing Technology, Guangdong University ofTechnology, Guangzhou 510090, P.R. China

ABSTRACT
Grinding and polishing are important steps in the production of decorative vitreous ceramic tiles. Different combinations of finishing wheels and polishing wheels are tested to optimize their selection. The results show that the surface glossiness depends not only on the surface quality before machining, but also on the characteristics of the ceramic tiles as well as the performance of grinding and polishing wheels. The performance of the polishing wheel is the key for a good final surface quality. The surface glossiness after finishing must be above 208 in order to get higher polishing quality because finishing will limit the maximum surface glossiness by polishing. The optimized combination of grinding and polishing wheels for all the steps will achieve shorter machining times and better surface quality. No obvious relationships are found between the hardness of ceramic tiles and surface quality or the wear of grinding wheels; therefore, the hardness of the ceramic tile cannot be used for evaluating its machinability.

Key Words: Ceramic tiles; Grinding wheel; Polishing wheel

INTRODUCTION
Ceramic tiles are the common decoration material for floors and walls of
hotel, office, and family buildings. Nowadays, polished vitreous ceramic tiles are more popular as decoration material than general vitreous ceramic tiles as they can

*Corresponding author. E-mail: cywang@

401
Copyright q 2002 by Marcel Dekker, Inc.
have a beautiful gloss on different colors. Grinding and polishing of ceramic tiles
play an important role in the surface quality, cost, and productivity of ceramic tiles
manufactured for decoration. The grinding and polishing of ceramic tiles are
carried out in one pass through polishing production line with many different
grinding wheels or by multi passes on a polishing machine, where different
grinding wheels are used.
Most factories utilize the grinding methods similar to those used for stone
machining although the machining of stone is different from that of ceramic tiles.
Vitreous ceramic tiles are thin, usually 5–8mm in thickness, and are a sintered
material,which possess high hardness, wear resistance, and brittleness. In general, the
sintering process causes surface deformation in the tiles. In themachining process, the
ceramic tiles are unfixed and put on tables. These characteristics will cause easy
breakage and lower surface quality if grinding wheel or grinding parameters are
unsuitable. To meet the needs of ceramic tiles machining, the machinery, grinding
parameters (pressure, feed speed, etc.), and grinding wheels (type and mesh size of
abrasive, bond, structure of grinding wheel, etc.) must be optimized.
Previous works have been reported in the field of grinding ceramic and
stone[1 – 4]. Only a few reports have mentioned ceramic tile machining[5 – 8], where
the grinding mechanism of ceramic tiles by scratching and grinding was studied. It
was pointed out that the grinding mechanism of ceramic tiles is similar to that of
other brittle materials. For vitreous ceramic tiles, removing the plastic deformation
grooves, craters (pores), and cracks are of major concern, which depends on the
micro-structure of the ceramic tile, the choice of grinding wheel and processing
parameters, etc. The residual cracks generated during sintering and rough grinding
processes, as well as thermal impact cracks caused by the transformation of quartz
crystalline phases are the main reasons of tile breakage during processing. Surface
roughness Ra and glossiness are different measurements of the surface quality. It is
suggested that the surface roughness can be used to control the surface quality of
rough grinding and semi-finish grinding processes, and the surface glossiness to
assess the quality of finishing and polishing processes. The characteristics of the
grinding wheels, abrasive mesh size for the different machining steps, machining
time, pressure, feed, and removing traces of grinding wheels will affect the
processing of ceramic tiles[9].
In this paper, based on the study of grinding mechanisms of ceramic tiles, the
manufacturing of grinding wheels is discussed. The actions and optimization of
grinding and polishing wheels for each step are studied in particular for manualpolishing
machines.

GRINDING AND POLISHING WHEELS FOR CERAMIC TILE
MACHINING

The machining of ceramic tiles is a volume-production process that uses
significant numbers of grinding wheels. The grinding and polishing wheels for

ceramic tile machining are different from those for metals or structural ceramics.
In this part, some results about grinding and polishing wheels are introduced for
better understanding of the processing of ceramic tiles.

Grinding and Polishing Wheels

Ceramic tiles machining in a manual-polishing machine can be divided into
four steps—each using different grinding wheels. Grinding wheels are marked as
2#, 3#, and 4# grinding wheels, and 0# polishing wheel; in practice, 2# and 3#
grinding wheels are used for flattening uneven surfaces. Basic requirements of
rough grinding wheels are long life, high removal rate, and lower price. For 2# and
3# grinding wheels, SiC abrasives with mesh #180 (#320) are bonded by
magnesium oxychloride cement (MOC) together with some porous fills,
waterproof additive, etc. The MOC is used as a bond because of its low price,
simple manufacturing process, and proper performance.
The 4# grinding wheel will refine the surface to show the brightness of ceramic
tile. The GC#600 abrasives and some special polishingmaterials, etc., are bonded by
MOC. In order to increase the performance such as elasticity, etc., of the grinding
wheel, the bakelite is always added. The 4# grinding wheels must be able to rapidly
eliminate all cutting grooves and increase the surface glossiness of the ceramic tiles.
The 0# polishing wheel is used for obtaining final surface glossiness, which
is made of fine Al2O3 abrasives and fill. It is bonded by unsaturated resin. The
polishing wheels must be able to increase surface glossiness quickly and make the
glossy ceramic tile surface permanent.

Manufacturing of Magnesium Oxychloride Cement Grinding Wheels

After the abrasives, the fills and the bond MOC are mixed and poured into the
models for grinding wheels, where the chemical reaction of MOC will solidify the
shape of the grinding wheels. The reaction will stop after 30 days but the hardness of
grinding wheel is essentially constant after 15 days. During the initial 15-day period,
the grinding wheels must be maintained at a suitable humidity and temperature.
For MOC grinding wheels, the structure of grinding wheel, the quality of
abrasives, and the composition of fill will affect their grinding ability. All the
factors related to the chemical reaction of MOC, such as the mole ratio of
MgO/MgCl2, the specific gravity of MgCl2, the temperature and humidity to care
the cement will also affect the performance of the MOC grinding wheels.

Mole Ratio of MgO/MgCl2
When MOC is used as the bond for the grinding wheels, hydration reaction
takes place between active MgO and MgCl2, which generates a hard
XMgeOHT2·YeMgCl2T·ZH2O phase. Through proper control of the mole ratio of
MgO/MgCl2, a reaction product with stable performance is formed. The bond is
composed of 5MgeOHT2·eMgCl2T·8H2O and 3MgeOHT2·eMgCl2T·8H2O: As the
former is more stable, optimization of the mole ratio of MgO/MgCl2 to produce
more 5MgeOHT2·eMgCl2T·8H2O is required. In general, the ideal range for the
mole ratio of MgO/MgCl2 is 4–6. When the contents of the active MgO and
MgCl2 are known, the quantified MgO and MgCl2 can be calculated.

Active MgO

The content of active MgO must be controlled carefully so that hydration
reaction can be successfully completed with more 5MgeOHT2·eMgCl2T·8H2O: If
the content of active MgO is too high, the hydration reaction time will be too short
with a large reaction heat, which increases too quickly. The concentrations of the
thermal stress can cause generation of cracks in the grinding wheel. On the
contrary, if the content of active MgO is too low, the reaction does not go to
completion and the strength of the grinding wheel is decreased.

Fills and Additives

The fills and additives play an important role in grinding wheels. Some porous fills must be added to 2# and 3# grinding wheels in order to improve the capacity to contain the grinding chips, and hold sufficient cutting grit. Waterproof additives such as sulfates can ensure the strength of grinding wheels in processing under water condition. Some fills are very effective in increasing the surface quality of ceramic tile, but the principle is not clear.

Manufacturing of Polishing Wheels
Fine Al2O3 and some soft polishing materials, such as Fe2O3, Cr2O3, etc., are mixed together with fills. Unsaturated resin is used to bond these powders, where a chemical reaction takes place between the resin and the hardener by means of an activator. The performance of polishing wheels depends on the properties of resin and the composition of the polishing wheel. In order to contain the fine chips, which are generated by micro-cutting, some cheap soluble salt can be fed into the coolant. On the surface of the polishing wheel, the salt will leave uniform pores, which not only increase the capacity to contain chips and self-sharpening of the polishing wheel, but also improves the contact situation between polishing wheel and ceramic tiles.

Experimental Procedure
Tests were carried out in a special manual grinding machine for ceramic
tiles. Two grinding wheels were fixed in the grinding disc that was equipped to the
grinding machine. The diameter of grinding disc was 255 mm. The rotating speed
of the grinding disc was 580 rpm. The grinding and polishing wheels are isosceles
trapezoid with surface area 31.5 cm2 (the upper edge: 2 cm, base edge: 5 cm,
height: 9 cm). The pressure was adjusted by means of the load on the handle for
different grinding procedures. A zigzag path was used as the moving trace for the
grinding disc. To maintain flatness and edge of the ceramic tiles, at least one third
of the tile must be under the grinding disc. During the grinding process, sufficient
water was poured to both cool and wash the grinding wheels and the tiles.
Four kinds of vitreous ceramic tiles were examined, as shown in Table 1.
Two different sizes of ceramic A, A400 (size: 400 ￡ 400 ￡ 5mm3T and A500
(size: 500 ￡ 500 ￡ 5mm3T were tested to understand the effect of the tile size. For
ceramic tile B or C, the size was 500 ￡ 500 ￡ 5mm3: The phase composition of the
tiles was determined by x-ray diffraction technique. Surface reflection glossiness
and surface roughness of the ceramic tiles and the wear of grinding wheels were measured.
The grinding and polishing wheels were made in-house. The 2# grinding
wheels with abrasives of mesh #150 and 3# grinding wheels with mesh #320 were
used during rough grinding. Using the ceramic tiles with different surface
toughness ground by the 2# grinding wheel for 180 sec, the action of the 3#
grinding wheels were tested. The ceramic tile was marked as A500-1 (or B500-1,
C500-1, A400-1) with higher initial surface toughness or A500-2 (or B500-2,
C500-2, A400-2) with lower initial surface toughness.
Two kinds of finishing wheels, 4#A and 4#B were made with the same structure, abrasivity, and process, but different composition of fills and additives. Only in 4#B, a few Al2O3, barium sulfate, and magnesium stearate were added for higher surface glossiness. The composition of the polishing wheels 0#A and 0#B were different as well. In 0#B, a few white alundum (average diameter 1mm),
barium sulfate, and chrome oxide were used as polishing additives, specially. After ground by 4#A (or 4#B) grinding wheel, the ceramic tiles were polished with 0#A (or 0#B). The processing combinations with 4# grinding wheels and 0#
Table 1. Properties of Ceramic Tiles
Ceramic Tiles
HV0.1
Crystalline
Grain Size
(mm)
Mullite
(vol.%)
Quartz
(vol.%)
Vitreous
Mass
(vol.%)
Porosity
(vol.%)
Pore Size
(mm)
A400,A500
661.0
10-30
32-40
15-18
35-40
3-5
5-20
B500
710.6
10-30
32-40
10-13
35-40
5-7
3-50
C500
614.2
10-30
12-15
10-13
35-40
3-5
5-30
polishing wheels were marked as 4#A–0#A, 4#A–0#B, 4#B–0#A, 4#B–0#B for each ceramic tile.
RESULTS AND DISCUSSIONS
Effects of 2# and 3# Grinding Wheels
Surface Quality

In rough grinding with a 2# grinding wheel, the surface roughness for all the tiles asymptotically decreases as the grinding time increases, see Fig. 1. The initial asymptote point of this curve represents the optimized rough grinding time, as continued grinding essentially has no effect on the surface roughness. In these tests, the surface roughness curves decrease with grinding time and become smooth at ,120 sec. The final surface quality for different kinds of ceramic tiles is slightly different. In terms of the initial size of the tile, the surface roughness of ceramic tile A400 e ￡ 400 ￡ 5mm3T is lower than that of A500 e500 ￡ 500 ￡ 5mm3T: The surface roughness of ceramic tile B500 rapidly drops as the grinding time increases.
Thus, it is easier to remove surface material from the hardest of the
three kinds of the ceramic tiles (Table 1). However, as the final surface roughness of ceramic tile A500 is the same as that of ceramic tile C500, the hardness of theceramic tile does not have a direct relationship with the final surface quality.
In the 3# grinding wheel step, all craters and cracks on the surface of ceramic tiles caused by the 2# grinding wheel must be removed. If residual cracks and craters exist, it will be impossible to get a high surface quality in the next step. The surface roughness obtained by the 2# grinding wheel will also affect the surface

Figure 1. Surface roughness of several ceramic tiles as a function of grinding time for 2# grinding
wheel.
quality of next grinding step by the 3# grinding wheel. In Fig. 2, the actions of the 3# grinding wheels are given using the ceramic tiles with different initial Ra, which were ground by the 2# grinding wheel for 180 sec. The curves