Debinderizer for rapidly removing binder from a green body

The disclosure relates to a system for removing binder from "green" bodies wherein debinding action takes place substantially uniformly throughout the sytem for large load as well as for small loads. This result is obtained by providing a plurality of shelves for holding the parts and providing turbulent atmosphere flow across all shelves with recirculation taking palce over a water fall in the system to provide both a water saturated atmosphere and removal of binder from the atmosphere and system simultaneously.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a debinderizer for rapidly removing binder from a 
green body composed of fine particles of metal or ceramic and a binder 
system without causing swelling of the binder system while within the 
interstices of the green body and for removal of substantially all carbon 
formed during removal of the binder caused by pyrolysis and/or other 
reasons and to the method of providing a beneficial atmosphere stream 
path. 
2. Description of the Prior Art 
The art of forming articles from metal and ceramic particulate material is 
well known and examples of such systems are represented in the prior art 
patents of Strivens, U.S. Pat. Nos. 2,939,199, Curry 4,011,291, Wiech 
4,404,166, the European application of Wiech (81100209.6, published July 
22, 1981), Wiech U.S. Pat. No. 4,661,315 and others. In accordance with 
the procedures set forth in the disclosures in the above noted patents and 
European application, debinderizing and sintering have proceeded without 
any substantial problem with varying degrees of speed as long as the 
debinderizer load was small relative to the load capacity of the 
debinderizer. However, it was found that a carbon build-up developed both 
on the surface of as well as within the part being formed for large loads 
as stated in the above noted Wiech U.S. application. This problem was 
minimized to a great degree and debinderizing speed increased by the 
addition of water to the system as stated in said Wiech U.S application 
using prior art debinderizers. However, upon inspection, it was noted that 
sintered parts positioned within the debinderizer and remote from the 
direct path of recirculating atmosphere therein did not benefit from the 
carbon reduction and debinding speed to the same extent as the parts which 
were directly in the path of the moving atmosphere. This presented a yield 
problem which was undesirable. It is therefore apparent that a system 
and/or procedure which will improve the yield without adding offsetting 
problems is highly desirable. 
BRIEF DESCRIPTION OF THE INVENTION 
In accordance with the present invention, the above noted problem is 
minimized and there is provided a debinderizer and atmosphere flow path 
wherein binder is rapidly removed from "green" parts at substantially all 
locations within the debinderizer and wherein yields obtained per unit 
volume of debinderizer are much larger than those obtained in prior art 
debinderizers. 
Briefly, in accordance with the present invention, there is provided a 
bebinderizer in the form of an oven having a plurality of shelves disposed 
one above the other to hold "green" parts. Openings are provided at 
opposite ends of each shelf to permit turbulent flow of the atmosphere 
along each shelf and over and around the "green" bodies sitting thereon at 
high speed. External atmosphere, such as air, as needed, enters the oven 
through a closable opening, mixes with recirculating atmosphere, and 
circulates over a water holding container and water fall to substantially 
saturate said atmosphere with water vapor. The saturated atmosphere is 
blown at high speed in a turbulent manner by a blower through a heater 
wherein the atmosphere is heated and then travels across the shelves in a 
direction parallel thereto to apply the saturated atmosphere in intimate 
contact with the green bodies, whereupon the atmosphere absorbs binder, 
leaves the shelf area, takes on external atmosphere as needed and 
recirculatres back over the water holding container and water fall system. 
The water holding container and water fall system comprises an upper water 
holding tank into which water flows from an external source, the 
temperature of which is substantially below the boiling point of the 
components of the binder system and possibly some or all of the products 
of binder decomposition. The container has a lower side wall over which 
the water eventually falls and travels along an incline to a lower 
container, the recirculating atmosphere passing over both containers and 
the incline to vaporize most of said water. The water in the containers is 
sufficiently cool to cause the volatilized binder and some or all of the 
products of binder decomposition to condense therein and eventually fall 
to the bottom of the lower container. These condensed components pass, in 
the liquid or solid state, from the lower container to an enclosed 
container external of the oven along with some of the water and atmosphere 
under the influence of an external blower, the gases in the lower 
container being driven therefrom by a blower. The external blower creates 
a partial vacuum in the external container which pulls the liquified 
binder out of the oven along with some of the water and oven atmosphere. 
The oven is encased in a metal housing with Kaowool, a ceramic fiber 
insulator with high temperature capability to about 2300.degree. F. being 
disposed between the housing and the oven to provide the insulation 
thereto. 
The above described arrangement provides a recirculating water saturated 
atmosphere which moves at high speed and passes evenly and around 
substantially all "green bodies" in the oven to provide a unifrom and high 
degree of binder removal and a high degree of water reaction with any 
carbon formed by pyrolytic decomposition of the binder or otherwise in 
conjunction with all of the "green" bodies in the system.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the Figure, there is a schematic showing of a debinderizer 
in accordance with the present invention. The debinderizer includes an 
outer steel housing 1, an oven 5 within the housing and insulation 3 
between the housing and the oven. The insulation can be any material which 
is capable of withstanding temperatures which will be observed within the 
oven. A preferred insulating material is a proprietary product known as 
Kaowool which is a ceramic fiber insulator with a high temperature 
capability of up to about 2300.degree. F. The oven 5 includes a closable 
opening 7 from the oven exterior thereinto through the oven outer surface 
9, the latter being formed of steel sheet. The oven 5 and debinderizer and 
preferably in the shape of a rectangular parallelepiped though the shape 
is not critical. For example, a spherical or ovoid shape can also be used. 
A plurality of stacked shelves 11 are positioned and secured within a shelf 
holder 13 having air passages 15 at opposite ends thereof to direct the 
travel of circulated atmosphere within the oven from one end of the shelf 
holder 13 to the other end thereof in a direction substantially parallel 
to the shelves 15, to thereby surround and remove binder from the "green" 
bodies disposed on the shelves. A heating element 17 is positioned within 
the oven 5, preferably in the path of atmosphere flow and just before the 
atmosphere stream enters the shelf holder 13. A blower 19 is positioned 
within the oven 5 and directs water saturated atmosphere toward the 
heating element 17 and also provides the atmosphere stream with the oven 
with an increased flow rate to provide a turbulent atmosphere stream when 
the stream passes over the "green" bodies on the shelves 11. 
A water source 21 is provided external of the housing 1 to provide water 
through the valve 23 to an upper container 25 positioned within the oven 5 
at the bottom thereof and directly in the atmosphere stream. The water 
will be sufficiently cool in order to cause condensation of binder and 
binder reaction products therein as is discussed hereinbelow. 
The container 25 has a lowered side wall 37 at the upstream side thereof 
with an incline 27 extending from the wall 37 to a lower container 29, 
overflow water from container 25 passing over the incline 27 to the 
container 29. The lower container 29 and the incline 27 are also 
positioned directly in the path of atmosphere flow in order to saturate or 
at least humidify the atmosphere as it passes thereover. Since atmosphere 
contacting the water in container 25 or 29 or on the incline 27 will 
normally have volatilized binder or reaction products of the pyrolytic 
decomposition of the binder therein, such volatilized products, where 
appropriate, will condense in the water and gradually flow, either in the 
liquid or solid state, to the bottom of container 29. 
A passageway 31 is provided at the base of the container 29 which empties 
into enclosed container 33 to pass liquid and solid binder and reaction 
products thereof from the bottom of container 29 to container 33. In 
addition, some atmosphere from oven 5 and water may pass along passageway 
31 to container 33. A blower 35 communicates with the interior of 
container 33 to provide a partial vacuum therein, thereby causing the 
materials noted above which flow in passageway 31 to be pulled into 
container 33. The container 33 will thereby be a collection point for 
spent binder and any non-gaseous reaction products of binder 
decomposition. Any volatiles that enter container 33 via passageway 31 
will be exhausted to the external atmosphere through or under the 
influence of blower 35. The bulk of any effluent particulates are retained 
in the water in container 33. 
In actual operation, "green" bodies of the type disclosed in the prior art, 
as noted hereinabove and elsewhere, are placed on the shelves 11, the 
heater 17 is operated according to a predetermined temperature profile and 
the blower 19 is operated to cause an atmosphere stream to pass from the 
blower, over the heater and then along the shelves 11 in a turbulent and 
high speed flow around the "green" bodies to remove any liquid binder on 
the surface thereof as well as products of binder decomposition. The 
atmosphere then travels out of the shelf area and past the air inlet 7, 
where it takes on air in an amount sufficient to compensate for any loss 
of air at passageway 31. The atmosphere stream then passes over the water 
in container 29, the incline 27 and the container 25 to pick up moisture 
and to permit any volatiles which condense at the temperature of the water 
to condense into the water at one of the water locations. The moisturized 
air will continue along the somewhat circular, continuous path and will 
gradually become more saturated with each pass of the water up to 
substantially the saturation point. The condensed volatiles as well as 
particulates, water and air will also pass to container 33 via passageway 
31 to remove binder and binder reaction products from the oven 5 on-line. 
As stated above, any particulates are retained in the water in container 
33. 
If desired, in the event an atmosphere other than air is required in the 
oven 5, the opening 7 can be closed and replaced with an input system of 
an appropriate atmosphere. For example, if an inert atmosphere is desired, 
an external tank of argon with a valve can be provided in place of the air 
input 7. In the case where a reducing atmosphere is required, the argon 
tank and valve can be supplemented with a hydrogen tank and valve. 
It can be seen that there has been provided a debinderising system and 
method wherein the atmosphere is forced at high speed and with turbulent 
flow over the surfaces of "green" bodies with all of the "green" bodies 
having substantially equal access to the atmosphere stream, thereby 
providing uniformity and a high final yield of parts relative to prior art 
systems. 
Though the invention has been described with respect to a specific 
preferred embodiment thereof, many variations and modifications will 
immediately become apparent to those skilled in the art. It is therefore 
the intention that the appended claims be interpreted as broadly as 
possible in view of the prior art to include all such variations and 
modification.