Boring or penetrating the earth – Enlargement of existing pilot throughbore requiring...
Reexamination Certificate
2001-07-11
2003-07-01
Neuder, William (Department: 3672)
Boring or penetrating the earth
Enlargement of existing pilot throughbore requiring...
C175S062000, C175S405000
Reexamination Certificate
active
06585062
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to underground drilling machines. More particularly, the present invention relates to reamers for use in horizontal directional drilling.
BACKGROUND OF THE INVENTION
Utility lines for water, electricity, gas, telephone, and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is subsequently back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular.
A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string about its longitudinal axis. The drill string comprises a series of drill pipes threaded together. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground.
In a typical horizontal directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. To remove cuttings and dirt during drilling, drilling fluid can be pumped by a pump system through the drill string, over a drill head (e.g., a cutting or boring tool) at the end of the drill string, and back up through the hole. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. Once the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface, completing a pilot bore.
The diameter of the pilot bore so constructed typically must be enlarged. To accomplish this, a reamer (sometimes called a backreamer) is attached to the drill string which is pulled back along the path of the pilot hole, thus reaming out the hole to a larger diameter. The reamer usually includes a reaming or cutting surface on which is mounted cutting teeth or other cutting or grinding elements. It is also common to attach a utility line or other conduit product to the reamer so that the product is pulled through the hole behind the reamer as the reamer enlarges the hole.
When utilizing standard backreaming techniques a backreamer is pulled longitudinally along the path of the pilot bore. Under certain conditions, however, the backreamer may tend to deviate from the path defined by the pilot bore. For instance, typically the pilot bore and drill string lie in an arcuate shape. Therefore the longitudinal force being exerted on the drill string tends to straighten the drill string, especially when soil conditions require increased levels of force on the drill string. This straightening tendency can affect the location of the backreamer by pulling the reamer higher. In some jobs the backreamer may move as much as 12 to 18 inches from the pilot bore. Such inaccuracy can have negative effects particularly when a utility or natural obstacle such as a river is being avoided.
In other situations, where large diameter bores are being formed, the weight of the backreamer can cause deviation from the pilot bore. A backreamer can only be moved longitudinally along the pilot bore at a rate in proportion to the drilling fluid being pumped to the reamer and out of the pilot bore. Therefore, longitudinal progress may be very slow. A heavy backreamer in the right soils will tend to drop lower than the pilot bore as it rotates quickly but moves slowly longitudinally.
Typically, the limiting factor in the speed of operation for a backreamer is the flow capacity of the pump system that pumps the drilling fluid. The backreamer should only displace soil at a rate in proportion to the amount of drilling fluid being pumped and removed from the pilot bore. Reamers may include mixing elements which assist in mixing the drilling fluid with the dirt and cuttings to achieve an easily displaceable consistency. The mixing elements rotate along with the reamer. The mixing function of the mixing elements and, therefore, the speed of the entire backreaming operation improves when the mixing elements are rotated at faster spinning speeds (rpms).
Faster spinning speeds also increase the total power transferred to the reamer. The total power transferred is a function of spinning speed multiplied by torque. By increasing the spinning speed of the drill string, more power can be delivered to the backreamer.
Faster spinning speeds, however, are not always desirable. Although spinning the backreamer at higher speeds improves mixing and delivers more power to the backreamer, faster or excessive speeds can cause instability of the assembly, resulting in fluctuations in the drive torque, torque spikes, and vibrations which deleteriously affect the cutting action of the cutting elements on the reaming surface of the backreamer. Spinning the cutting surface at faster speeds may also cause difficulty in controlling the backreamer.
These drawbacks become more acute with larger backreamers, particularly for backreamers which produce bores in excess of 18 inches. The speed of an individual cutting element on a backreamer is determined by the rotational speed of the backreamer and the distance from the center of the backreamer to the cutting element. Therefore, cutting elements on larger backreamers will move faster at any given spinning speed than cutting elements on smaller backreamers. As a result, the cutting action of a large backreamer is more susceptible to the inefficient effects of faster spinning speeds.
A backreamer, then, may perform several functions including: mechanically cutting, grinding and loosening the soil to enlarge the pilot hole diameter, directing drilling fluid to assist in the cutting action, mixing the loosened soil with the drilling fluid such that the resulting slurry is a consistency that will flow out of the bore when displaced by whatever product is to be pulled in, and transferring the longitudinal force required to pull the product through the hole.
The amount of torque necessary to rotate a backreamer depends on several factors which include: the outer diameter of the backreamer, the difference between the diameter of the pilot hole and the outer diameter of the backreamer, the type of soil, the speed at which the backreamer is being rotated, and the longitudinal force being applied to the backreamer.
SUMMARY OF THE INVENTION
One aspect of the present invention relates to a backreamer assembly adapted to be rotated by a drill string. The backreamer assembly includes a reaming surface and a torque transfer gear system that transfers torque from the drill string to the reaming surface of the backreamer. The torque transfer gear system is preferably configured to drive the reaming surface at a different rotational speed than the drill string. In one embodiment, the torque transfer gear system includes one or more reduction gears that rotate the reaming surface at a slower rotational speed than the drill string.
Another aspect of the present invention relates to a planetary gear train for a backreamer. The planetary gear train allows the cutting surface of the backreamer to spin at a slower speed than the speed at which the drill string rotates, thereby supplying increased power to the backreamer without the deleterious effects of instability and excessive vibrations. The planetary gear train includes a sun gear which is coupled to the drill string and rotates at the same speed as the drill string. The sun gear engages a number of planet gears which in turn engage a ring gear. The ring gear has an outer reaming surface. By adjusting the relative diameters of the ring and sun gears, the reaming surface of the ring gear can be rotated at a smaller or larger fraction of the speed of the drill string
Rempe Scott
Rozendaal Peter C.
LandOfFree
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