Page 60 - Diamond Products Catalog

SURFACE SET BITS
Boart Longyear offers surface set diamond bits in a variety of sizes. Surface set bits can be very cost effective in soft sedimentary rocks. Boart LongyearTM surface set bits are produced with stepped profiles, which generate the best performance in soft ground conditions.
Matrix and Diamond Grades
Using advanced power metallurgy technology, coupled with years of field experience, Boart Longyear has developed a high performance matrix that is suitable for virtually all common drilling conditions. This matrix is standard
on Boart Longyear surface set products and provides for the highest diamond-holding characteristics. Boart Longyear matches
this special matrix with the highest-quality, unprocessed, natural drilling diamonds, specifically for use in its core bits. These diamonds have enough strength to handle the hardest ground conditions and result in the longest lasting bits.
The diamond grade and amount of diamond play a role in operating parameters as well. Typically, driller’s use sufficient weight on bit to ensure the bit cuts freely at an acceptable penetration rate (usually 2 – 6 in/min, [5 – 15 cm/min]). In the absence of experience in the conditions to be drilled, an approximation of maximum weight on bit when using high-quality diamonds is given by the following formula:
Maximum Weight on Bit (lb) = Carat Weight x Average Number of Stones/Carat x 7
Maximum Weight on Bit (kg) = Carat Weight x Average Number of Stones/Carat x 3.2
Example: NQ BIT - 16 carats, 45/55 stones/carat
Maximum Suggested Weight on Bit = 16 x 50 x 7 = 5,600 lb
16 x 50 x 3.2 = 2 560 kg
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Crown Profiles
The profile of the bit face or crown is important because it affects drilling speed, hole deviation, and core recovery. There is a wide choice of profiles for surface set bits which cover all common drilling conditions. As a rule, multi-step bits, standardized by the DCDMA, drill fastest and provide excellent core recovery. For hard and/or broken conditions where round or semi-flat profiles would be preferred, SSUMXTM impregnated bits produce better performance.
Waterways
Waterways are usually shallow in surface set bits to provide even cooling and flushing throughout the face. When using Boart Longyear's QTM3 (triple-tube) core barrels to minimize core washing, such as in soft, friable formations, face discharge ports are recommended.
STEP-TYPE (STP)
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