Heat resistant pad for use with rear facilities of aluminium extrusion pressing machine

Disclosed herein is a heat resistant pad which comprises a plurality layers of batt mixtures essentially consisting of carbon fibers and aromatic polyamide fibers, the layers of batt mixtures being superposed and entangled to integrate into a felt-like structure by way of needle punching. A heat resistant pad of such constitution has a property of adequate flexibility, wear resistance, impact resistance, frictional coefficient and cushioning property for use with rear facilities of an aluminium extrusion pressing machine. Also disclosed is a heat resistant pad coated and impregnated with a silicone resin to improve wear resistance and impact resistance.

BACKGROUND OF THE INVENTION 
(i) Field of the Invention 
Thin invention concerns a heat resistant pad for use with a cooling table 
or a spacer in the extrusion forming process in the fields of non-ferrous 
metal industries such as for aluminium or in heat treatment processes in 
ceramic industries or the like. 
More specifically, it relates to a felt-structured heat resistant pad for 
use with rear facilities of an aluminium extrusion pressing machine, such 
as a canister, initial table, run-out table, lift arm and cooling table. 
(ii) Description of the Prior Art 
Rear facilities of an aluminium extrusion pressing machine are used for 
receiving or transporting the extruded products at high temperature 
(550.degree.-600.degree. C.) shaped through an extrusion die. It is 
required that the heat resistant pad for use with such facilities satisfy 
the following criteria 
(1) capability of withstanding high temperatures of about 600.degree. C., 
(2) not scratching the surface of the extruded products, 
(3) adequate cushioning property, with no grooved traces left by the 
extruded products, 
(4) adequate friction coefficient so as not to allow excess slip of the 
extruded products, 
(5) low heat conductivity, 
(6) low hygroscopic property, 
(7) no generation of decomposed gases nor deposition by melting upon 
contact with the extruded product and 
(8) sufficient wear resistance and impact resistance under high temperature 
conditions. 
However, since conventional heat resistant pads are made of plates of 
materials such as synthetic or natural carbon, woven fabrics of asbestos 
or glass fibers and plates of teflon resin, they suffer from the following 
disadvantages: 
(a) Heat Resistant Pads Made of Plates of Synthetic or Natural Carbon 
Since they lack in wear resistance and tend to have grooved traces at the 
surface thereof formed by the extruded products, the succeeding extruded 
products are often caught in the traces and damaged. Further, since they 
have high heat conductivity, the portions of the extruded products 
undergoing cooling will be at different temperatures depending on whether 
or not they are in contact with the surfaces of the pad, which temperature 
differences result in an altering of the crystal structure of aluminium. 
Consequently, cooling produces remarkable dimensional errors, formation of 
pits in the rapidly cooled portions of the extruded products depending on 
their cross sectional profile, or results in clouding and so-called black 
spots or white spots in the subsequent surface treatment or like 
additional steps. Furthermore, since they have an excessively low 
frictional coefficient, the extruded products can not be transported due 
to excess slip when such material are used in a lift arm or a cooling 
table. 
(b) Heat Resistant Pads Made of Woven Fabrics of Asbestos or Glass Fibers 
While they are usually woven into cloth and affixed to a metallic core in 
use, they lack in flexibility and tend to damage the extruded products. 
Further, they are susceptible to injury from impact applied from the edges 
of the extruded products, and the pad body inevitably undergoes attrition 
to form powdery dusts which worsen the working atmosphere. 
(c) Heat Resistant Pads Made of Teflon Resin 
Just like in (a) above, poor wear resistance often leads to injury by the 
extruded products and insufficient frictional coefficient causes trouble 
in the transportation of the extruded products. Furthermore, the resin may 
possibly melt and to deposit on the extruded products. 
SUMMARY OF THE INVENTION 
The object of this invention is to overcome the foregoing problems and 
provide a heat resistant pad having flexibility, cushioning, wear 
resistance and impact resistance coupled with an adequate frictional 
coefficient. The pad of the present invention, intended for use with rear 
facilities of an aluminium extrusion pressing machine, if formed of a 
plurality of batts essentially consisting of carbon fibers which have 
excellent heat-resistance and flexibility and which cause no damage to 
extruded products admixed with aromatic polyamide fibers which have 
excellent heat resistance and low heat conductivity and which serve to 
reduce the heat conductivity of the batts to as low as possible, the batts 
being superposed into a plurality of layers and entangled together into an 
integral felt-like structure by needle punching. 
A further object of the invention is to provide a heat resistant pad having 
flexibility, cushioning property, wear resistance and impact resistance 
coupled with an adequate frictional coefficient, and for use with rear 
facilities of an aluminium extrusion pressing machine, formed of a 
plurality of batts essentially consisting of carbon fibers which have 
excellent heat-resistance, flexibility and which causes no damage to 
extruded products admixed with aromatic polyamide fibers having excellent 
heat resistance and low heat conductivity to reduce the overall heat 
conductivity of the batts to as low as possible, the batts being 
superposed into a plurality of layers and entangled together into an 
integral felt-like structure by needle punching, and in which at least one 
surface layer of the pad body is coated and impregnated with a silicone 
resin heat resistant paint to improve wear resistance and impact 
resistance while maintaining the initial form of the pad body to elongate 
the service life of the pad.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
This invention is to be described by way of preferred embodiments shown in 
FIG. 1 to FIG. 6D. 
FIG. 1 shows a pad body 5 mixed fiber batts 3, each batt essentially 
consisting of carbon fibers 1 admixed with aromatic polyamide fibers 2, 
batts 3 being superimposed into a plurality of layers and entangled 
together into an integral felt-like structure by way of needle punching 4. 
For the convenience of the illustration, the carbon fibers 1 are 
represented by the blank areas, the aromatic polyamide fibers 2 by zigzag 
solid lines and the needle punching 4 by parallel vertical lines. 
The purposes of admixing the carbon fibers 1 with the aromatic polyamide 
fibers 2 are to compensate the defective abrasion resistance and heat 
conductivity and easily damaged nature of the carbon fibers, as well as to 
enhance the entanglement of the fibers in the course of the needle 
punching. Accordingly, it is preferred to set the mixing ratio of the 
carbon fibers 1 to the aromatic polyamide fiber 2 within a range of 
8-6:2-4 and, particularly, within a range of 7:3. If the relative content 
of aromatic polyamide fibers is below the specified range, the foregoing 
purposes can not be satisfied. While on the other hand, if the relative 
content of the polyamide fibers exceeds the specified range, the heat 
resistance of the pad body 5 per se is reduced, because the upper limit of 
the heat resistivity for the aromatic polyamide fibers is from 200.degree. 
to 300.degree. C., which is significantly lower than the heat resistant 
temperature required for the pad body 5. 
The aromatic polyamide fibers referred to above include "methaphenylene 
isophthalamide" commercially available under the tradename of "CONEX" and 
"NOMEX" or "methaphenylene terephthalamide" commercially available under 
the tradename of "KEVLAR". 
In the mixed fiber batts 3 subjected to the needle punching 4, since the 
carbon fibers 1 and the aromatic polyamide fibers 2 are entangled with 
each other in random directions in each of the layers as well as between 
the layers, and the fibers are oriented in the direction of the punching, 
the strength of the pad against the frictional force of the aluminium 
extruded products (not shown) is further increased. 
It is also desired that the pad body 5 have a density from 0.25 to 0.6 
g/cm.sup.3 after the needle punching. In other words, when the thickness 
of the pad body is between 7 to 12 mm, it is desirous that the weight of 
the pad body be between 3000 to 4000 g/m.sup.2. If the density exceeds the 
specified range, the pad lacks in flexibility and tends to damage the 
extruded products; moreover, the heat conductivity of the pad is 
increased. While on the other hand, if the density is lower than the 
specified range, the toughness is lost, whereby the pad is liable to be 
injured by the extruded products and the wear resistivity is reduced. 
FIG. 2 shows one example of a pad body 5 comprising mixed fiber batts 3 
essentially consisting of carbon fibers 1 admixed with aromatic polyamide 
fibers 2, which are superimposed into a plurality of layers and entangled 
together into an integral felt-like structure by way of needle punching 4 
to form a pad body 5, and in which at least the upper surface layer of the 
body is coated and impregnated with a silicone resin heat resistant paint 
6 (represented the fine dots). 
The silicone resin heat resistant paint 6 to be applied for the coating and 
impregnation of pad body 5 may be silicone resin alone or a mixture 
consisting essentially of silicone resin and heat resistant reinforcing 
material such as carbon, graphite or metal oxide admixed therewith, which 
is despersed and mixed in a solvent such as xylene. The coating film 
formed from such a paint has excellent heat resistance at temperatures as 
high as 600.degree.-800.degree. C., and the coating on the constituent 
fibers of the heat resistant pad with the paint film can advantageously 
increase the wear and impact resistance of the heat resistant pad while 
maintaining the heat resistance of the carbon fibers. 
The paint may be coated and impregnated by way of any conventional means 
such as spraying, impregnation, brush coating or roller coating and the 
pad may be coated only on the surface in contact with the extruded 
products, over the side surface also or over its entire surface and, 
depending on the case, may be impregnated through the entire pad. In any 
case, it is important to control the coating amount so as not to impair 
the flexibility and the cushioning property of the pad. Preferable amounts 
of silicone resin are such that the solid matter remained after 
volatilization is 3-15 wt% of the weight of the pad body to be coated. 
Curing after drying for the paint is, preferably, carried out at 
180.degree.-200.degree. C. for about 30-40 min. 
The heat resistant pad according to the invention can be fabricated, for 
use, into various configurations such as plate, conveyor belt, tube and 
roll, depending on the application and intended use in a canister, initial 
table, run-out table, lift arm, cooling table or the like of an aluminium 
extrusion pressing machine. 
FIG. 3 shows one sample of a pad body 5 in which mixed fiber batts 3 are 
superimposed one on another in such a way that the mixing ratio of the 
aromatic polyamide fibers 2 to the carbon fibers 1 in each of the mixtures 
is increased stepwise upper surface layer to the lower layer. In this 
case, while the mixing ratio has to be within the specified range at least 
in the uppermost layer, the mixing ratio may be reversed that is, the 
amount of the aromatic polyamide fibers may be greater than that of the 
carbon fibers toward the lower layer. Such a gradation is effective for 
reducing the heat conductivity. 
FIGS. 4A, 4B, 4C and 4D show various embodiments, in which at least one 
heat resistant foundation fabric 7 is interposed between the layers of the 
mixed fiber batts, or appended to the bottom surface of the lowermost 
layer of the mixed fiber batts 3. The material usable for the foundation 
fabric 7 may be carbon fibers, aromatic polyamide fibers, glass fibers, or 
admixtures thereof so long as the fibers are heat resistant, with the 
aromatic polyamide fibers being most preferred in view of the strength. 
Interposition or attachment of the foundation fabric 7 is effective for 
increasing the strength of the pad body 5. 
FIGS. 5A, 5B, 5C and 5D show various embodiments, in which at least one 
batt 8 solely consisting of aromatic polyamide fibers (shown by oblique 
lines in the drawings) is interposed between the layers of the mixed fiber 
batts, or appended to the bottom surface of the lowermost layer of the 
mixed fiber batts 3. This is effective for reducing the heat conductivity 
of pad body 5 and reinforcing the mixed fiber batts in strength. 
FIGS. 6A, 6B, 6C and 6D show various embodiments, in which at least one set 
of a heat resistant foundation fabric 7 and a batt 8 solely consisting of 
aromatic polyamide fibers, joined to each other, is interposed between the 
layers of the mixed fiber batts or appended to the bottom surface of the 
lowermost layer of the mixed fiber batts 3. In this case, both of the 
increase in the strength of the pad body 5 and the reduction in the heat 
conductivity are achieved. 
Though in the embodiments of FIG. 3 to FIG. 6, silicone resin coating and 
impregnation is not illustrated, however, when a silicone resin heat 
resistant paint is coated and impregnated, an improved effect can be 
obtained in wear resistance and impact resistance to protect the pad body. 
As described above, according to this invention, since the pad body is 
comprised essentially of carbon fibers, it can well withstand the high 
temperature of aluminium extruded products (550.degree.-600.degree. C.) 
which are freshly extruded from the die onto the initial table or the 
run-out table. Further, since aromatic polyamide of low heat conductivity 
is admixed with carbon fibers and they are needle-punched into a felt-like 
structure, the heat conductivity of the pad can be maintained low 
irrespective of the use of the carbon fibers. As the result, no 
differences in temperature, upon cooling, occur between the portions in 
contact and those not in contact with aluminium extruded products, as 
compared with conventional carbon plates, whereby improvement in the 
quality of the extruded products can be expected, as well as improved wear 
resistivity and prolonged service life in the pad. 
Further, since the felt-like structure is obtained by needle punching the 
plural layers of the mixed fiber batts essentially consisting of carbon 
fibers admixed with aromatic polyamide fibers, the heat resistant pad of 
this invention possesses adequate flexibility and cushioning property, 
which prevent scratches to the extruded products and the grooved traces 
formed by the extruded products, in the conventional carbon plate. In 
addition, since the present pad has an adequate frictional coefficient, it 
can effectively transport the extruded products when used in a lift arm or 
a cooling table. 
Furthermore, since the pad according to this invention comprises a fiber 
assembly, it is utterly free from problems such as cracking or chipping 
due to the impact and heat of the extruded products and can be used stably 
for a long time. 
Moreover, silicone resin coating and impregnation is effective to 
strengthen the pad body in wear resistance and impact resistance while 
maintaining adequate flexibility, cushioning property, frictional 
coefficient as well as the initial form of the pad body, and, thereby, 
further elongated service life can be obtained.