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Improving the Efficiency of Grinding Soft or Rubbery Polymers Utilizing Titanium Carbo Nitride Coated High Speed Rotor and Stator

IP.com Disclosure Number: IPCOM000126210D
Publication Date: 2005-Jul-07
Document File: 6 page(s) / 2M

Publishing Venue

The IP.com Prior Art Database

Abstract

The rapid and continuous deterioration in performance of polymer grinding can be improved by coating a rotor and stator set with a material which significantly increases hardness and resistance to wear. Hence the process of vapor deposition of Titanium CarboNitride (TiCN) onto 316 SS metal greatly improved the efficiency of polymer grinding by reducing wear and thereby improving polymer grinding productivity.

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Improving the Efficiency of Grinding Soft or Rubbery Polymers Utilizing Titanium Carbo Nitride Coated High Speed Rotor and Stator

Background

A new method has been perfected in a laboratory in reference to achieving a more efficiently ground or comminuted poly alpha-olefin polymer (PAO).  PAOs are very soft polymers having a glass transition temperature (Tg) on the order of -60 to -80oC and have typically been ground via cryogenic grinding techniques in years past.  The new grinding methodology described herein, may be found in U.S. Patent 6,894,088, Motier, et al.  The patent describes a process for producing polymer drag reducing agent (DRA) slurries without cryogenic temperature. More specifically, the equipment mentioned in the patent is a high speed rotor and stator homogenizer including the MEGASHEAR from Ross Mixers, Inc.

The rotor and stator was hardened by a coating of Titanium Carbo Nitride.  In doing so the hardened steel becomes much more efficient at comminuting polymer and the lifetime of the unit is dramatically extended.

Polymer granules from 6-20 mm size can be ground to a mean particle size of 200 microns with a non solvent carrier in this particular operation.   The rotor (Figure 3) operates at 10,000 rpm with a tip speed of 15,700 feet/min. The rotor and stator (Figure 1) has small tolerance for effective grinding, thus the need for the initial feeding of granulated PAO.  

The material of construction of the rotor and stator is stainless steel -SS 316. Titanium Carbo Nitride Coating (TiCN) is applied on SS 316 using a Physical Vapor Deposition (PVD) coating technology.  The subsequent TiCN coating layer has a hardness of HRC-90. Its hardness and toughness in combination with much improved wear resistance ensures that it finds it principal application for coating relatively lower wear resistant materials.

Fig 1. Stator

Fig 2. Stator Close View

The uncoated rotor and stator made of traditional 316 SS wears significantly during a high speed polymer grinding operation as mentioned above. Hence the tolerance between the rotor and stator increases (gap widens due to wear) leading to reduction in grinding efficiency. A concomitant effect is the increase in grinding time for achieving the desired particle size. Also, this type of wear is permanent and attempts at re-machining the rotor and stator is almost impossible due to the complex construction of the rotor and stator. Given that the cost of the rotor and stator set is considerable, it is not economically feasible to replace the set when the performance deteriorates.

Fig 3. Rotor

Fig 4. Rotor Close View

The grinding heads (a set of rotor and stator) without the hardening treatment could...