2-Part Silicone Putty – aka: Dental Impression Materials
Silicone Packing — aka: “dental impression material” a term that is an artifact of development work done more than 20 years ago. The SoundHorse 2-part silicone packing is specifically designed for the rigors of hoof packing application and is “gas permeable”. This unique property allows treatment materials mixed with the silicone (copper sulfate) to slowly pass thru the cured silicone as a treatment.
There are a variety of hoof packings offered from suppliers to the equine “podiatry” market segment. Farriers, Veterinarians and Clinicians have to choose between urethanes and silicones, each of which has unique performance properties. This paper will address Silicone Hoof Packing only.
Question: HOW does a farrier or veterinarian choose among the many 2-part silicone products?
Answer: The only useful method to differentiate silicone packing is “hardness”.
This paper will attempt to clarify the question, provide a chart to differentiate the currently offered products and explain a simple industry testing method used to generate the data.
Discussion of Results: (see charts & graph… Tests conducted at room temp of ~ 68°F)
The commercially available 2-part silicones tested fell into two (2) broad groupings that were a “Softer” hardness at ~ 25-30 Shore “A” and “Firmer” hardness at ~ 45-50+ Shore “A”. These two (2) groupings were demonstrably different and could be easily differentiated by most farriers and vets. It should be noted that product name and color are of little use when differentiating silicone hardness between suppliers. Only Sound Horse prints the durometer of their products on their packaging to indicate “hardness”.
Chart of silicone hoof packing materials commonly used in Equine applications
Test results for silicone materials available to farriers, vets & clinicians for hoof repair and cushioning.
Graph of Results
Durometer is one of several ways to demonstrate the hardness of a material, which is defined as the material’s resistance to permanent indentation. It is named for instrument maker Albert F. Shore, developer of the measurement device called the durometer in the 1920s. The term durometer is often used to refer to the measurement, as well as the instrument itself. Durometer is typically used as a measure of hardness in polymers, elastomers and rubbers.
There are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the ASTM D2240 type A and type D scales. The “A” scale is for softer plastics, while the “D” scale is for harder ones. Each scale results in a value between 0 and 100, with higher values indicating a harder material.
Method of Measurement
Durometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its viscoelastic properties, the shape of the presser foot, and the duration of the test. ASTM D2240 durometer allows for a measurement of the initial hardness, or the indentation hardness after a given period of time. The basic test requires applying the force in a consistent manner, without shock, while measuring the hardness (depth of the indentation). If a timed hardness is desired, force is applied for the required time and then read. The material under test should be a minimum of 6.4 mm (0.25 inch) thick.
Testing Equipment – Shore Durometer Type A and D
The final value of the hardness depends on the depth of the indenter’s penetration. If the indenter penetrates 2.5mm or more into the material, the durometer is 0 for that scale. If it does not penetrate at all, then the durometer is 100 for that scale. It is for this reason that multiple scales exist. Durometer is a dimensionless quantity, and there is no simple relationship between a material’s durometer in one scale, and its durometer in any other scale, or by any other hardness test.
Durometer of a Typical Material
An automotive tire tread is one of the rubber or polymer objects categorized by durometer hardness. Tires typically range from 50A to 70A, depending on their application.