US 5,328,713 AGranted

Precise regulation of fluidized bed weight in pyrolytically coating substrates

AssigneeCarbon Implants, Inc.

InventorsMichael R. Emken, James A. Accuntius, David S. Wilde

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Abstract

Precise control of pyrocarbon being coated upon an object in a fluidized particle bed is achieved by monitoring the weight change of the fluidized particle bed over a period of time. Measurement of such weight change is truly representative of bed size in such a coater, which is a most important factor in achieving the desired characteristics of the pyrocarbon being deposited. By monitoring the bed size by repeatedly determining such changes in the weight, compensating adjustments are made by either adding additional particles to the bed or by changing the rate at which particles are withdrawn so that precise coating characteristics are achieved, and coatings can be deposited within very close thickness tolerances.

Claims20

Dependent claims

A method of carefully controlling the deposition of a substance onto a substrate while being levitated in a fluidized bed of particles, said deposition being carried out in an enclosure through which a gaseous atmosphere is caused to flow upward, which method comprises

(a) establishing a bed of particles in fluidized condition in said enclosure with at least one substrate to be coated being levitated within said fluidized bed, said levitation being effected by the upward flow of said gaseous atmosphere,
(b) heating said particles and said substrate to an operating temperature and including a pyrolytically-decomposable component within said gaseous atmosphere such that pyrolysis of said component occurs to cause a pyrolytic substance to be deposited at said operating temperature upon said substrate and upon said particles, both of which are being levitated,
(c) withdrawing particles from said bed in a controlled manner,
(d) adding feed particles to said bed in a controlled manner, which feed particles have an average size that is less than the average size of the particles being withdrawn,
(e) monitoring the weight of said bed to determine changes in the weight of said bed over a period of time, and
(f) altering either the rate at which particles are withdrawn from said bed or the rate at which particles are added to said bed or both in response to said determined weight changes so as to precisely regulate deposition rate over time and thereby produce a precise pyrolytic coating upon said substrate being coated.

3 more elements

Apparatus for depositing a pyrolytic substance on a substrate while it is being levitated in a fluidized bed of particles, which apparatus comprises

a coating enclosure,
means for flowing a gaseous mixture upward through said enclosure to maintain a bed of particles in fluidized condition in said enclosure and levitate at least one substrate to be coated within said fluidized bed,
heating means for maintaining said substrate and said fluidized bed of particles at a temperature so that pyrolysis of a component of said gaseous mixture occurs in said fluidized bed to cause the pyrolytic substance to be deposited upon said substrate and upon said particles,
means for withdrawing particles from said fluidized bed,
means for adding particles to said fluidized bed having an average size that is less than the average size of the particles being withdrawn therefrom,
means for monitoring the weight of said fluidized bed so as to determine changes in the weight of said fluidized bed, and
means for changing the rate at which particles are withdrawn from said fluidized bed or the rate at which feed particles are added to said bed or both in response to said weight changes so determined, whereby deposition upon said substrate being coated is precisely regulated over time.

4 more elements

Dependencies are inferred from the claim text.