Method of forming slide gate valve parts

DETAILED DESCRIPTION The periclase refractory grain used will contain at least 90%, preferably 95% or more MgO.
It should be a relatively high strength grain; that is to say, it preferably contains CaO and SiO.
sub.
2 in such proportions that the lime:silica ratio is 2 or more.
For example the grain will contain 2% or more CaO and preferably 1% or less SiO.
sub.
2.
Although it is not certain, and applicant does not wish to be bound to a particular theory, it is believed that the polyphosphate reacts with the lime (CaO) in the periclase to form a major bond, and that better bonding is achieved with a relatively high lime periclase grain.
In addition, the grain will contain minor amounts of normal impurities such as A1.
sub.
2 O.
sub.
3 and Fe.
sub.
2 O.
sub.
3.
The grain will preferably be of relatively high density, for example it will have a bulk specific gravity (bsg) of 3.
4 or more.
For the grain to be of high bsg, it should have a relatively low boron content, for example less than 0.
1% B.
sub.
2 O.
sub.
3 .
The grain will be sized to achieve good packing, as is well-known in this art.
For example, it will all be smaller than 3.
3 mm (i.
e.
, pass a 6 mesh screen), and about 25% of it will be smaller than 44 microns (i.
e.
, pass a 325 mesh screen).
The long chain glassy polyphosphate used will be one of several well-known materials of commerce.
For reasons of economy, it will generally be a sodium polyphosphate, but other varieties can be used.
As is well-known, these polyphosphates have the general chemical formula Na.
sub.
n+2 P.
sub.
n O.
sub.
3n+1 where "n", the number of phosphorous atoms in the chain, is at least 4.
It is preferred that the polyphosphate used in this invention have an average chain length of about 20, for example 21.
The use of these materials as bonds for refractories is shown in U.
S.
Pat.
No.
3,304,187.
Preferably the polyphosphate is used in granular (e.
g.
, all less than 2.
4 mm--all passing an 8 mesh screen), anhydrous form (i.
e.
, showing an ignition loss of less than 1%).
However, a water solution of the material can be used, with appropriate adjustment of the amount used to allow for the actual amount of polyphosphate in the solution